diff --git a/docs/source/conf.py b/docs/source/conf.py
index e521b3d6..3bf42c53 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -16,8 +16,6 @@ import os
 import sys
 sys.path.insert(0, os.path.abspath('../../'))
 
-import sphinx_rtd_theme
-
 # -- Project information -----------------------------------------------------
 
 project = 'fastNLP'
@@ -27,7 +25,7 @@ author = 'xpqiu'
 # The short X.Y version
 version = ''
 # The full version, including alpha/beta/rc tags
-release = '1.0'
+release = '2.0'
 
 
 # -- General configuration ---------------------------------------------------
diff --git a/docs/source/fastNLP.core.rst b/docs/source/fastNLP.core.rst
index 5c941e55..b70b6798 100644
--- a/docs/source/fastNLP.core.rst
+++ b/docs/source/fastNLP.core.rst
@@ -13,10 +13,10 @@ fastNLP.core.dataset
 .. automodule:: fastNLP.core.dataset
     :members:
 
-fastNLP.core.field 
+fastNLP.core.fieldarray
 -------------------
 
-.. automodule:: fastNLP.core.field
+.. automodule:: fastNLP.core.fieldarray
     :members:
 
 fastNLP.core.instance 
@@ -25,10 +25,10 @@ fastNLP.core.instance
 .. automodule:: fastNLP.core.instance
     :members:
 
-fastNLP.core.loss 
+fastNLP.core.losses
 ------------------
 
-.. automodule:: fastNLP.core.loss
+.. automodule:: fastNLP.core.losses
     :members:
 
 fastNLP.core.metrics 
@@ -49,12 +49,6 @@ fastNLP.core.predictor
 .. automodule:: fastNLP.core.predictor
     :members:
 
-fastNLP.core.preprocess 
-------------------------
-
-.. automodule:: fastNLP.core.preprocess
-    :members:
-
 fastNLP.core.sampler 
 ---------------------
 
diff --git a/fastNLP/core/batch.py b/fastNLP/core/batch.py
index 1bb26129..442d1154 100644
--- a/fastNLP/core/batch.py
+++ b/fastNLP/core/batch.py
@@ -5,21 +5,19 @@ import torch
 class Batch(object):
     """Batch is an iterable object which iterates over mini-batches.
 
-    ::
-        for batch_x, batch_y in Batch(data_set, batch_size=16, sampler=SequentialSampler()):
+        Example::
 
+            for batch_x, batch_y in Batch(data_set, batch_size=16, sampler=SequentialSampler()):
+                # ...
+
+    :param dataset: a DataSet object
+    :param batch_size: int, the size of the batch
+    :param sampler: a Sampler object
+    :param as_numpy: bool. If True, return Numpy array. Otherwise, return torch tensors.
 
     """
 
     def __init__(self, dataset, batch_size, sampler, as_numpy=False):
-        """
-
-        :param dataset: a DataSet object
-        :param batch_size: int, the size of the batch
-        :param sampler: a Sampler object
-        :param as_numpy: bool. If True, return Numpy array. Otherwise, return torch tensors.
-
-        """
         self.dataset = dataset
         self.batch_size = batch_size
         self.sampler = sampler
diff --git a/fastNLP/core/dataset.py b/fastNLP/core/dataset.py
index 52dac2fc..c798a422 100644
--- a/fastNLP/core/dataset.py
+++ b/fastNLP/core/dataset.py
@@ -118,7 +118,7 @@ class DataSet(object):
     def __len__(self):
         """Fetch the length of the dataset.
 
-        :return int length:
+        :return length:
         """
         if len(self.field_arrays) == 0:
             return 0
@@ -170,7 +170,7 @@ class DataSet(object):
     def delete_field(self, name):
         """Delete a field based on the field name.
 
-        :param str name: the name of the field to be deleted.
+        :param name: the name of the field to be deleted.
         """
         self.field_arrays.pop(name)
 
@@ -182,14 +182,14 @@ class DataSet(object):
     def get_all_fields(self):
         """Return all the fields with their names.
 
-        :return dict field_arrays: the internal data structure of DataSet.
+        :return field_arrays: the internal data structure of DataSet.
         """
         return self.field_arrays
 
     def get_length(self):
         """Fetch the length of the dataset.
 
-        :return int length:
+        :return length:
         """
         return len(self)
 
@@ -232,14 +232,14 @@ class DataSet(object):
     def get_input_name(self):
         """Get all field names with `is_input` as True.
 
-        :return list field_names: a list of str
+        :return field_names: a list of str
         """
         return [name for name, field in self.field_arrays.items() if field.is_input]
 
     def get_target_name(self):
         """Get all field names with `is_target` as True.
 
-        :return list field_names: a list of str
+        :return field_names: a list of str
         """
         return [name for name, field in self.field_arrays.items() if field.is_target]
 
@@ -294,8 +294,9 @@ class DataSet(object):
         """Split the dataset into training and development(validation) set.
 
         :param float dev_ratio: the ratio of test set in all data.
-        :return DataSet train_set: the training set
-                DataSet dev_set: the development set
+        :return (train_set, dev_set):
+                train_set: the training set
+                dev_set: the development set
         """
         assert isinstance(dev_ratio, float)
         assert 0 < dev_ratio < 1
@@ -326,7 +327,7 @@ class DataSet(object):
         :param List[str] or Tuple[str] headers: headers of the CSV file
         :param str sep: delimiter in CSV file. Default: ","
         :param bool dropna: If True, drop rows that have less entries than headers.
-        :return DataSet dataset:
+        :return dataset: the read data set
 
         """
         with open(csv_path, "r") as f:
@@ -370,7 +371,7 @@ class DataSet(object):
         """Load a DataSet object from pickle.
 
         :param str path: the path to the pickle
-        :return DataSet data_set:
+        :return data_set:
         """
         with open(path, 'rb') as f:
             return pickle.load(f)
diff --git a/fastNLP/core/fieldarray.py b/fastNLP/core/fieldarray.py
index 5fa8276e..c1a2db1c 100644
--- a/fastNLP/core/fieldarray.py
+++ b/fastNLP/core/fieldarray.py
@@ -2,20 +2,18 @@ import numpy as np
 
 
 class FieldArray(object):
-    """FieldArray is the collection of Instances of the same Field.
-    It is the basic element of DataSet class.
+    """``FieldArray`` is the collection of ``Instance``s of the same field.
+    It is the basic element of ``DataSet`` class.
+
+    :param str name: the name of the FieldArray
+    :param list content: a list of int, float, str or np.ndarray, or a list of list of one, or a np.ndarray.
+    :param int padding_val: the integer for padding. Default: 0.
+    :param bool is_target: If True, this FieldArray is used to compute loss.
+    :param bool is_input: If True, this FieldArray is used to the model input.
 
     """
 
     def __init__(self, name, content, padding_val=0, is_target=None, is_input=None):
-        """
-
-        :param str name: the name of the FieldArray
-        :param list content: a list of int, float, str or np.ndarray, or a list of list of one, or a np.ndarray.
-        :param int padding_val: the integer for padding. Default: 0.
-        :param bool is_target: If True, this FieldArray is used to compute loss.
-        :param bool is_input: If True, this FieldArray is used to the model input.
-        """
         self.name = name
         if isinstance(content, list):
             content = content
diff --git a/fastNLP/core/instance.py b/fastNLP/core/instance.py
index dc65fa82..a2877a8f 100644
--- a/fastNLP/core/instance.py
+++ b/fastNLP/core/instance.py
@@ -1,23 +1,22 @@
 class Instance(object):
-    """An Instance is an example of data. It is the collection of Fields.
+    """An Instance is an example of data.
+        Example::
+            ins = Instance(field_1=[1, 1, 1], field_2=[2, 2, 2])
+            ins["field_1"]
+            >>[1, 1, 1]
+            ins.add_field("field_3", [3, 3, 3])
 
-    ::
-        Instance(field_1=[1, 1, 1], field_2=[2, 2, 2])
+        :param fields: a dict of (str: list).
 
     """
 
     def __init__(self, **fields):
-        """
-
-        :param fields: a dict of (str: list).
-        """
         self.fields = fields
 
     def add_field(self, field_name, field):
         """Add a new field to the instance.
 
         :param field_name: str, the name of the field.
-        :param field:
         """
         self.fields[field_name] = field
 
diff --git a/fastNLP/core/losses.py b/fastNLP/core/losses.py
index 057b03f2..04f8b73e 100644
--- a/fastNLP/core/losses.py
+++ b/fastNLP/core/losses.py
@@ -13,6 +13,9 @@ from fastNLP.core.utils import get_func_signature
 
 
 class LossBase(object):
+    """Base class for all losses.
+
+    """
     def __init__(self):
         self.param_map = {}
         self._checked = False
@@ -68,10 +71,9 @@ class LossBase(object):
         #                     f"positional argument.).")
 
     def _fast_param_map(self, pred_dict, target_dict):
-        """
-
-        Only used as inner function. When the pred_dict, target is unequivocal. Don't need users to pass key_map.
+        """Only used as inner function. When the pred_dict, target is unequivocal. Don't need users to pass key_map.
             such as pred_dict has one element, target_dict has one element
+
         :param pred_dict:
         :param target_dict:
         :return: dict, if dict is not {}, pass it to self.evaluate. Otherwise do mapping.
@@ -265,27 +267,22 @@ def _prepare_losser(losser):
 
 
 def squash(predict, truth, **kwargs):
-    """To reshape tensors in order to fit loss functions in pytorch
-
-    :param predict	: Tensor, model output
-    :param truth	: Tensor, truth from dataset
-    :param **kwargs : extra arguments
+    """To reshape tensors in order to fit loss functions in PyTorch.
 
+    :param predict: Tensor, model output
+    :param truth: Tensor, truth from dataset
+    :param **kwargs: extra arguments
     :return predict , truth: predict & truth after processing
     """
     return predict.view(-1, predict.size()[-1]), truth.view(-1, )
 
 
 def unpad(predict, truth, **kwargs):
-    """To process padded sequence output to get true loss
-    Using pack_padded_sequence() method
-    This method contains squash()
+    """To process padded sequence output to get true loss.
 
-    :param predict	: Tensor, [batch_size , max_len , tag_size]
-    :param truth	: Tensor, [batch_size , max_len]
-    :param **kwargs : extra arguments, kwargs["lens"] is expected to be exsist
-        kwargs["lens"] : list or LongTensor, [batch_size]
-                      the i-th element is true lengths of i-th sequence
+    :param predict: Tensor, [batch_size , max_len , tag_size]
+    :param truth: Tensor, [batch_size , max_len]
+    :param kwargs: kwargs["lens"] is a list or LongTensor, with size [batch_size]. The i-th element is true lengths of i-th sequence.
 
     :return predict , truth: predict & truth after processing
     """
@@ -299,15 +296,11 @@ def unpad(predict, truth, **kwargs):
 
 
 def unpad_mask(predict, truth, **kwargs):
-    """To process padded sequence output to get true loss
-    Using mask() method
-    This method contains squash()
+    """To process padded sequence output to get true loss.
 
-    :param predict	: Tensor, [batch_size , max_len , tag_size]
-    :param truth	: Tensor, [batch_size , max_len]
-    :param **kwargs : extra arguments, kwargs["lens"] is expected to be exsist
-        kwargs["lens"] : list or LongTensor, [batch_size]
-                      the i-th element is true lengths of i-th sequence
+    :param predict: Tensor, [batch_size , max_len , tag_size]
+    :param truth: Tensor, [batch_size , max_len]
+    :param kwargs: kwargs["lens"] is a list or LongTensor, with size [batch_size]. The i-th element is true lengths of i-th sequence.
 
     :return predict , truth: predict & truth after processing
     """
@@ -318,14 +311,11 @@ def unpad_mask(predict, truth, **kwargs):
 
 
 def mask(predict, truth, **kwargs):
-    """To select specific elements from Tensor
-    This method contains squash()
+    """To select specific elements from Tensor. This method calls ``squash()``.
 
-    :param predict	: Tensor, [batch_size , max_len , tag_size]
-    :param truth	: Tensor, [batch_size , max_len]
-    :param **kwargs : extra arguments, kwargs["mask"] is expected to be exsist
-        kwargs["mask"] : ByteTensor, [batch_size , max_len]
-                      the mask Tensor , the position that is 1 will be selected
+    :param predict: Tensor, [batch_size , max_len , tag_size]
+    :param truth: Tensor, [batch_size , max_len]
+    :param **kwargs: extra arguments, kwargs["mask"]: ByteTensor, [batch_size , max_len], the mask Tensor. The position that is 1 will be selected.
 
     :return predict , truth: predict & truth after processing
     """
@@ -343,13 +333,11 @@ def mask(predict, truth, **kwargs):
 
 
 def make_mask(lens, tar_len):
-    """to generate a mask that select [:lens[i]] for i-th element
-    embezzle from fastNLP.models.sequence_modeling.seq_mask
-
-    :param lens		: list or LongTensor, [batch_size]
-    :param tar_len	: int
+    """To generate a mask over a sequence.
 
-    :return mask 	: ByteTensor
+    :param lens: list or LongTensor, [batch_size]
+    :param tar_len: int
+    :return mask: ByteTensor
     """
     lens = torch.LongTensor(lens)
     mask = [torch.ge(lens, i + 1) for i in range(tar_len)]
diff --git a/fastNLP/core/metrics.py b/fastNLP/core/metrics.py
index 07ebe3fe..388f3e84 100644
--- a/fastNLP/core/metrics.py
+++ b/fastNLP/core/metrics.py
@@ -13,6 +13,24 @@ from fastNLP.core.utils import seq_lens_to_masks
 
 
 class MetricBase(object):
+    """Base class for all metrics.
+
+    ``MetricBase`` handles validity check of its input dictionaries - ``pred_dict`` and ``target_dict``.
+    ``pred_dict`` is the output of ``forward()`` or prediction function of a model.
+    ``target_dict`` is the ground truth from DataSet where ``is_target`` is set ``True``.
+    ``MetricBase`` will do the following type checks:
+
+        1. whether self.evaluate has varargs, which is not supported.
+        2. whether params needed by self.evaluate is not included in ``pred_dict``, ``target_dict``.
+        3. whether params needed by self.evaluate duplicate in ``pred_dict``, ``target_dict``.
+        4. whether params in ``pred_dict``, ``target_dict`` are not used by evaluate.(Might cause warning)
+
+    Besides, before passing params into self.evaluate, this function will filter out params from output_dict and
+    target_dict which are not used in self.evaluate. (but if **kwargs presented in self.evaluate, no filtering
+    will be conducted.)
+    However, in some cases where type check is not necessary, ``_fast_param_map`` will be used.
+
+    """
     def __init__(self):
         self.param_map = {}  # key is param in function, value is input param.
         self._checked = False
@@ -71,10 +89,9 @@ class MetricBase(object):
         raise NotImplemented
 
     def _fast_param_map(self, pred_dict, target_dict):
-        """
-
-        Only used as inner function. When the pred_dict, target is unequivocal. Don't need users to pass key_map.
+        """Only used as inner function. When the pred_dict, target is unequivocal. Don't need users to pass key_map.
             such as pred_dict has one element, target_dict has one element
+
         :param pred_dict:
         :param target_dict:
         :return: dict, if dict is not {}, pass it to self.evaluate. Otherwise do mapping.
@@ -177,6 +194,9 @@ class MetricBase(object):
 
 
 class AccuracyMetric(MetricBase):
+    """Accuracy Metric
+
+    """
     def __init__(self, pred=None, target=None, seq_lens=None):
         super().__init__()
 
@@ -186,10 +206,9 @@ class AccuracyMetric(MetricBase):
         self.acc_count = 0
 
     def _fast_param_map(self, pred_dict, target_dict):
-        """
-
-        Only used as inner function. When the pred_dict, target is unequivocal. Don't need users to pass key_map.
+        """Only used as inner function. When the pred_dict, target is unequivocal. Don't need users to pass key_map.
             such as pred_dict has one element, target_dict has one element
+
         :param pred_dict:
         :param target_dict:
         :return: dict, if dict is not None, pass it to self.evaluate. Otherwise do mapping.
@@ -230,7 +249,7 @@ class AccuracyMetric(MetricBase):
                 torch.Size([B,]), torch.Size([B,]), torch.Size([B, max_len]), torch.Size([B, max_len])
         :param seq_lens: List of (torch.Tensor, or numpy.ndarray). Element's can be:
                 None, None, torch.Size([B], torch.Size([B]). ignored if masks are provided.
-        :return: dict({'acc': float})
+
         """
         # TODO 这里报错需要更改，因为pred是啥用户并不知道。需要告知用户真实的value
         if not isinstance(pred, torch.Tensor):
@@ -269,6 +288,11 @@ class AccuracyMetric(MetricBase):
             self.total += np.prod(list(pred.size()))
 
     def get_metric(self, reset=True):
+        """Returns computed metric.
+
+        :param bool reset: whether to recount next time.
+        :return evaluate_result: {"acc": float}
+        """
         evaluate_result = {'acc': round(self.acc_count / self.total, 6)}
         if reset:
             self.acc_count = 0
@@ -308,34 +332,31 @@ def _prepare_metrics(metrics):
 
 
 def accuracy_topk(y_true, y_prob, k=1):
-    """Compute accuracy of y_true matching top-k probable
-    labels in y_prob.
+    """Compute accuracy of y_true matching top-k probable labels in y_prob.
 
-        :param y_true: ndarray, true label, [n_samples]
-        :param y_prob: ndarray, label probabilities, [n_samples, n_classes]
-        :param k: int, k in top-k
-        :return :accuracy of top-k
-    """
+    :param y_true: ndarray, true label, [n_samples]
+    :param y_prob: ndarray, label probabilities, [n_samples, n_classes]
+    :param k: int, k in top-k
+    :returns acc: accuracy of top-k
 
+    """
     y_pred_topk = np.argsort(y_prob, axis=-1)[:, -1:-k - 1:-1]
     y_true_tile = np.tile(np.expand_dims(y_true, axis=1), (1, k))
     y_match = np.any(y_pred_topk == y_true_tile, axis=-1)
     acc = np.sum(y_match) / y_match.shape[0]
-
     return acc
 
 
 def pred_topk(y_prob, k=1):
     """Return top-k predicted labels and corresponding probabilities.
 
-
-        :param y_prob: ndarray, size [n_samples, n_classes], probabilities on labels
-        :param k: int, k of top-k
-    :returns
+    :param y_prob: ndarray, size [n_samples, n_classes], probabilities on labels
+    :param k: int, k of top-k
+    :returns (y_pred_topk, y_prob_topk):
         y_pred_topk: ndarray, size [n_samples, k], predicted top-k labels
         y_prob_topk: ndarray, size [n_samples, k], probabilities for top-k labels
-    """
 
+    """
     y_pred_topk = np.argsort(y_prob, axis=-1)[:, -1:-k - 1:-1]
     x_axis_index = np.tile(
         np.arange(len(y_prob))[:, np.newaxis],
diff --git a/fastNLP/core/optimizer.py b/fastNLP/core/optimizer.py
index fddafbad..145f117c 100644
--- a/fastNLP/core/optimizer.py
+++ b/fastNLP/core/optimizer.py
@@ -2,6 +2,11 @@ import torch
 
 
 class Optimizer(object):
+    """
+
+        :param model_params: a generator. E.g. ``model.parameters()`` for PyTorch models.
+        :param kwargs: additional parameters.
+    """
     def __init__(self, model_params, **kwargs):
         if model_params is not None and not hasattr(model_params, "__next__"):
             raise RuntimeError("model parameters should be a generator, rather than {}.".format(type(model_params)))
@@ -10,13 +15,14 @@ class Optimizer(object):
 
 
 class SGD(Optimizer):
-    def __init__(self, lr=0.001, momentum=0, model_params=None):
-        """
+    """
 
         :param float lr: learning rate. Default: 0.01
         :param float momentum: momentum. Default: 0
-        :param model_params: a generator. E.g. model.parameters() for PyTorch models.
-        """
+        :param model_params: a generator. E.g. ``model.parameters()`` for PyTorch models.
+    """
+
+    def __init__(self, lr=0.001, momentum=0, model_params=None):
         if not isinstance(lr, float):
             raise TypeError("learning rate has to be float.")
         super(SGD, self).__init__(model_params, lr=lr, momentum=momentum)
@@ -30,13 +36,14 @@ class SGD(Optimizer):
 
 
 class Adam(Optimizer):
-    def __init__(self, lr=0.001, weight_decay=0, betas=(0.9, 0.999), eps=1e-8, amsgrad=False, model_params=None):
-        """
+    """
 
         :param float lr: learning rate
         :param float weight_decay:
-        :param model_params: a generator. E.g. model.parameters() for PyTorch models.
-        """
+        :param model_params: a generator. E.g. ``model.parameters()`` for PyTorch models.
+    """
+
+    def __init__(self, lr=0.001, weight_decay=0, betas=(0.9, 0.999), eps=1e-8, amsgrad=False, model_params=None):
         if not isinstance(lr, float):
             raise TypeError("learning rate has to be float.")
         super(Adam, self).__init__(model_params, lr=lr, betas=betas, eps=eps, amsgrad=amsgrad,
diff --git a/fastNLP/core/sampler.py b/fastNLP/core/sampler.py
index 766d71a7..67ec2a8d 100644
--- a/fastNLP/core/sampler.py
+++ b/fastNLP/core/sampler.py
@@ -20,8 +20,8 @@ def convert_to_torch_tensor(data_list, use_cuda):
 class BaseSampler(object):
     """The base class of all samplers.
 
-        Sub-classes must implement the __call__ method.
-        __call__ takes a DataSet object and returns a list of int - the sampling indices.
+        Sub-classes must implement the ``__call__`` method.
+        ``__call__`` takes a DataSet object and returns a list of int - the sampling indices.
     """
 
     def __call__(self, *args, **kwargs):
@@ -32,8 +32,12 @@ class SequentialSampler(BaseSampler):
     """Sample data in the original order.
 
     """
-
     def __call__(self, data_set):
+        """
+
+        :param DataSet data_set:
+        :return result: a list of integers.
+        """
         return list(range(len(data_set)))
 
 
@@ -41,13 +45,23 @@ class RandomSampler(BaseSampler):
     """Sample data in random permutation order.
 
     """
-
     def __call__(self, data_set):
+        """
+
+            :param DataSet data_set:
+            :return result: a list of integers.
+        """
         return list(np.random.permutation(len(data_set)))
 
 
 class BucketSampler(BaseSampler):
+    """
+
+        :param int num_buckets: the number of buckets to use.
+        :param int batch_size: batch size per epoch.
+        :param str seq_lens_field_name: the field name indicating the field about sequence length.
 
+    """
     def __init__(self, num_buckets=10, batch_size=32, seq_lens_field_name='seq_lens'):
         self.num_buckets = num_buckets
         self.batch_size = batch_size
diff --git a/fastNLP/core/tester.py b/fastNLP/core/tester.py
index ef3780a0..48e1f090 100644
--- a/fastNLP/core/tester.py
+++ b/fastNLP/core/tester.py
@@ -1,5 +1,3 @@
-from collections import defaultdict
-
 import torch
 from torch import nn
 
@@ -15,7 +13,16 @@ from fastNLP.core.utils import get_func_signature
 
 
 class Tester(object):
-    """An collection of model inference and evaluation of performance, used over validation/dev set and test set. """
+    """An collection of model inference and evaluation of performance, used over validation/dev set and test set.
+
+        :param DataSet data: a validation/development set
+        :param torch.nn.modules.module model: a PyTorch model
+        :param MetricBase metrics: a metric object or a list of metrics (List[MetricBase])
+        :param int batch_size: batch size for validation
+        :param bool use_cuda: whether to use CUDA in validation.
+        :param int verbose: the number of steps after which an information is printed.
+
+    """
 
     def __init__(self, data, model, metrics, batch_size=16, use_cuda=False, verbose=1):
         super(Tester, self).__init__()
@@ -49,6 +56,11 @@ class Tester(object):
             self._predict_func = self._model.forward
 
     def test(self):
+        """Start test or validation.
+
+        :return eval_results: a dictionary whose keys are the class name of metrics to use, values are the evaluation results of these metrics.
+
+        """
         # turn on the testing mode; clean up the history
         network = self._model
         self._mode(network, is_test=True)
@@ -60,8 +72,8 @@ class Tester(object):
                     _move_dict_value_to_device(batch_x, batch_y, device=self._model_device)
                     pred_dict = self._data_forward(self._predict_func, batch_x)
                     if not isinstance(pred_dict, dict):
-                        raise TypeError(f"The return value of {get_func_signature(self._predict_func)} " 
-                                                         f"must be `dict`, got {type(pred_dict)}.")
+                        raise TypeError(f"The return value of {get_func_signature(self._predict_func)} "
+                                        f"must be `dict`, got {type(pred_dict)}.")
                     for metric in self.metrics:
                         metric(pred_dict, batch_y)
                 for metric in self.metrics:
diff --git a/fastNLP/core/trainer.py b/fastNLP/core/trainer.py
index bf32fa6c..3e8360d2 100644
--- a/fastNLP/core/trainer.py
+++ b/fastNLP/core/trainer.py
@@ -27,39 +27,37 @@ from fastNLP.core.utils import get_func_signature
 
 
 class Trainer(object):
-    """Main Training Loop
-
     """
-    def __init__(self, train_data, model, loss=None, metrics=None, n_epochs=3, batch_size=32, print_every=50,
-                 validate_every=-1, dev_data=None, use_cuda=False, save_path=None,
-                 optimizer=Adam(lr=0.01, weight_decay=0), check_code_level=0,
-                 metric_key=None, sampler=RandomSampler(), use_tqdm=True):
-        """
-
         :param DataSet train_data: the training data
         :param torch.nn.modules.module model: a PyTorch model
         :param LossBase loss: a loss object
-        :param MetricBase or List[MetricBase] metrics: a metric object or a list of metrics
+        :param MetricBase metrics: a metric object or a list of metrics (List[MetricBase])
         :param int n_epochs: the number of training epochs
         :param int batch_size: batch size for training and validation
         :param int print_every: step interval to print next training information. Default: -1(no print).
         :param int validate_every: step interval to do next validation. Default: -1(validate every epoch).
         :param DataSet dev_data: the validation data
-        :param use_cuda:
-        :param save_path: file path to save models
+        :param bool use_cuda: whether to use CUDA in training.
+        :param str save_path: file path to save models
         :param Optimizer optimizer: an optimizer object
-        :param int check_code_level: level of FastNLP code checker. -1: don't check, 0: ignore. 1: warning. 2: strict.
+        :param int check_code_level: level of FastNLP code checker. -1: don't check, 0: ignore. 1: warning. 2: strict.\\
             `ignore` will not check unused field; `warning` when warn if some field are not used; `strict` means
             it will raise error if some field are not used.
         :param str metric_key: a single indicator used to decide the best model based on metric results. It must be one
             of the keys returned by the FIRST metric in `metrics`. If the overall result gets better if the indicator gets
-            smaller, add a `-` character in front of the string. For example
-                ::
+            smaller, add "-" in front of the string. For example::
+
                     metric_key="-PPL"   # language model gets better as perplexity gets smaller
-        :param sampler: method used to generate batch data.
-        :param use_tqdm: boolean, use tqdm to show train progress.
 
-        """
+        :param BaseSampler sampler: method used to generate batch data.
+        :param bool use_tqdm: whether to use tqdm to show train progress.
+
+    """
+
+    def __init__(self, train_data, model, loss=None, metrics=None, n_epochs=3, batch_size=32, print_every=50,
+                 validate_every=-1, dev_data=None, use_cuda=False, save_path=None,
+                 optimizer=Adam(lr=0.01, weight_decay=0), check_code_level=0,
+                 metric_key=None, sampler=RandomSampler(), use_tqdm=True):
         super(Trainer, self).__init__()
 
         if not isinstance(train_data, DataSet):
@@ -141,30 +139,30 @@ class Trainer(object):
     def train(self, load_best_model=True):
         """
 
-        开始训练过程。主要有以下几个步骤
-        for epoch in range(num_epochs):
-            (1) 使用Batch从DataSet中按批取出数据，并自动对DataSet中dtype为float, int的fields进行padding。并转换为Tensor。非
-                    float，int类型的参数将不会被转换为Tensor，且不进行padding
-            for batch_x, batch_y in Batch(DataSet):
-                # batch_x中为设置为input的field
-                # batch_y中为设置为target的field
-                (2) 将batch_x的数据送入到model.forward函数中，并获取结果
-                (3) 将batch_y与model.forward的结果一并送入loss中计算loss
-                (4) 获取到loss之后，进行反向求导并更新梯度
-        if dev_data is not None:
-            根据metrics进行evaluation，并根据是否提供了save_path判断是否存储模型
-
-        :param load_best_model: 该参数只有在初始化提供了dev_data的情况下有效，如果True, trainer将在返回之前重新加载dev表现最好的
+        开始训练过程。主要有以下几个步骤::
+
+            对于每次循环
+                1. 使用Batch从DataSet中按批取出数据，并自动对DataSet中dtype为float, int的fields进行padding。并转换为Tensor。
+                非float，int类型的参数将不会被转换为Tensor，且不进行padding。
+                for batch_x, batch_y in Batch(DataSet)
+                    # batch_x中为设置为input的field
+                    # batch_y中为设置为target的field
+                    2. 将batch_x的数据送入到model.forward函数中，并获取结果
+                    3. 将batch_y与model.forward的结果一并送入loss中计算loss
+                    4. 获取到loss之后，进行反向求导并更新梯度
+            如果测试集不为空
+                根据metrics进行evaluation，并根据是否提供了save_path判断是否存储模型
+
+        :param bool load_best_model: 该参数只有在初始化提供了dev_data的情况下有效，如果True, trainer将在返回之前重新加载dev表现最好的
             模型参数。
+        :return results: 返回一个字典类型的数据, 内含以下内容::
 
-        将会返回一个字典类型的数据, 内含以下内容：
             seconds: float, 表示训练时长
             以下三个内容只有在提供了dev_data的情况下会有。
             best_eval: Dict of Dict, 表示evaluation的结果
             best_epoch: int，在第几个epoch取得的最佳值
             best_step: int, 在第几个step(batch)更新取得的最佳值
 
-        return dict:
         """
         results = {}
         try:
diff --git a/fastNLP/core/vocabulary.py b/fastNLP/core/vocabulary.py
index e8cc0e22..50a79d24 100644
--- a/fastNLP/core/vocabulary.py
+++ b/fastNLP/core/vocabulary.py
@@ -41,13 +41,13 @@ class Vocabulary(object):
         vocab.update(word_list)
         vocab["word"]
         vocab.to_word(5)
+
+    :param int max_size: set the max number of words in Vocabulary. Default: None
+    :param int min_freq: set the min occur frequency of words in Vocabulary. Default: None
+
     """
 
     def __init__(self, max_size=None, min_freq=None, unknown='<unk>', padding='<pad>'):
-        """
-        :param int max_size: set the max number of words in Vocabulary. Default: None
-        :param int min_freq: set the min occur frequency of words in Vocabulary. Default: None
-        """
         self.max_size = max_size
         self.min_freq = min_freq
         self.word_count = Counter()
@@ -78,6 +78,7 @@ class Vocabulary(object):
         """Add a single word into the vocabulary.
 
         :param str word: a word or token.
+
         """
         self.add(word)
 
@@ -86,11 +87,12 @@ class Vocabulary(object):
         """Add a list of words into the vocabulary.
 
         :param list word_lst: a list of strings
+
         """
         self.update(word_lst)
 
     def build_vocab(self):
-        """Build 'word to index' dict, and filter the word using `max_size` and `min_freq`.
+        """Build a mapping from word to index, and filter the word using ``max_size`` and ``min_freq``.
 
         """
         self.word2idx = {}
@@ -111,7 +113,7 @@ class Vocabulary(object):
         self.rebuild = False
 
     def build_reverse_vocab(self):
-        """Build 'index to word' dict based on 'word to index' dict.
+        """Build "index to word" dict based on "word to index" dict.
 
         """
         self.idx2word = {i: w for w, i in self.word2idx.items()}
@@ -146,10 +148,9 @@ class Vocabulary(object):
             raise ValueError("word {} not in vocabulary".format(w))
 
     def to_index(self, w):
-        """ Turn a word to an index.
-            If w is not in Vocabulary, return the unknown label.
+        """ Turn a word to an index. If w is not in Vocabulary, return the unknown label.
 
-        :param str w:
+        :param str w: a word
         """
         return self.__getitem__(w)