diff --git a/fastNLP/core/predictor.py b/fastNLP/core/predictor.py
index 802661ef..c83b2069 100644
--- a/fastNLP/core/predictor.py
+++ b/fastNLP/core/predictor.py
@@ -27,8 +27,8 @@ class Predictor(object):
         self.batch_output = []
         self.pickle_path = pickle_path
         self._task = task  # one of ("seq_label", "text_classify")
-        self.index2label = load_pickle(self.pickle_path, "id2class.pkl")
-        self.word2index = load_pickle(self.pickle_path, "word2id.pkl")
+        self.label_vocab = load_pickle(self.pickle_path, "class2id.pkl")
+        self.word_vocab = load_pickle(self.pickle_path, "word2id.pkl")
 
     def predict(self, network, data):
         """Perform inference using the trained model.
@@ -82,7 +82,7 @@ class Predictor(object):
         :return data_set: a DataSet instance.
         """
         assert isinstance(data, list)
-        return create_dataset_from_lists(data, self.word2index, has_target=False)
+        return create_dataset_from_lists(data, self.word_vocab, has_target=False)
 
     def prepare_output(self, data):
         """Transform list of batch outputs into strings."""
@@ -97,14 +97,14 @@ class Predictor(object):
         results = []
         for batch in batch_outputs:
             for example in np.array(batch):
-                results.append([self.index2label[int(x)] for x in example])
+                results.append([self.label_vocab.to_word(int(x)) for x in example])
         return results
 
     def _text_classify_prepare_output(self, batch_outputs):
         results = []
         for batch_out in batch_outputs:
             idx = np.argmax(batch_out.detach().numpy(), axis=-1)
-            results.extend([self.index2label[i] for i in idx])
+            results.extend([self.label_vocab.to_word(i) for i in idx])
         return results
 
 
diff --git a/fastNLP/fastnlp.py b/fastNLP/fastnlp.py
index c76e6681..e683950d 100644
--- a/fastNLP/fastnlp.py
+++ b/fastNLP/fastnlp.py
@@ -69,7 +69,7 @@ class FastNLP(object):
         :param model_dir: this directory should contain the following files:
             1. a pre-trained model
             2. a config file
-            3. "id2class.pkl"
+            3. "class2id.pkl"
             4. "word2id.pkl"
         """
         self.model_dir = model_dir
@@ -99,10 +99,10 @@ class FastNLP(object):
         print("Restore model hyper-parameters {}".format(str(model_args.data)))
 
         # fetch dictionary size and number of labels from pickle files
-        word2index = load_pickle(self.model_dir, "word2id.pkl")
-        model_args["vocab_size"] = len(word2index)
-        index2label = load_pickle(self.model_dir, "id2class.pkl")
-        model_args["num_classes"] = len(index2label)
+        word_vocab = load_pickle(self.model_dir, "word2id.pkl")
+        model_args["vocab_size"] = len(word_vocab)
+        label_vocab = load_pickle(self.model_dir, "class2id.pkl")
+        model_args["num_classes"] = len(label_vocab)
 
         # Construct the model
         model = model_class(model_args)
diff --git a/reproduction/chinese_word_segment/run.py b/reproduction/chinese_word_segment/run.py
index d0a22e84..0d5ae8c1 100644
--- a/reproduction/chinese_word_segment/run.py
+++ b/reproduction/chinese_word_segment/run.py
@@ -32,7 +32,7 @@ def infer():
     # fetch dictionary size and number of labels from pickle files
     word2index = load_pickle(pickle_path, "word2id.pkl")
     test_args["vocab_size"] = len(word2index)
-    index2label = load_pickle(pickle_path, "id2class.pkl")
+    index2label = load_pickle(pickle_path, "class2id.pkl")
     test_args["num_classes"] = len(index2label)
 
 
@@ -105,7 +105,7 @@ def test():
     # fetch dictionary size and number of labels from pickle files
     word2index = load_pickle(pickle_path, "word2id.pkl")
     test_args["vocab_size"] = len(word2index)
-    index2label = load_pickle(pickle_path, "id2class.pkl")
+    index2label = load_pickle(pickle_path, "class2id.pkl")
     test_args["num_classes"] = len(index2label)
 
     # load dev data
diff --git a/reproduction/pos_tag_model/train_pos_tag.py b/reproduction/pos_tag_model/train_pos_tag.py
index 87a9f7e8..15164130 100644
--- a/reproduction/pos_tag_model/train_pos_tag.py
+++ b/reproduction/pos_tag_model/train_pos_tag.py
@@ -33,7 +33,7 @@ def infer():
     # fetch dictionary size and number of labels from pickle files
     word2index = load_pickle(pickle_path, "word2id.pkl")
     test_args["vocab_size"] = len(word2index)
-    index2label = load_pickle(pickle_path, "id2class.pkl")
+    index2label = load_pickle(pickle_path, "class2id.pkl")
     test_args["num_classes"] = len(index2label)
 
     # Define the same model
@@ -105,7 +105,7 @@ def test():
     # fetch dictionary size and number of labels from pickle files
     word2index = load_pickle(pickle_path, "word2id.pkl")
     test_args["vocab_size"] = len(word2index)
-    index2label = load_pickle(pickle_path, "id2class.pkl")
+    index2label = load_pickle(pickle_path, "class2id.pkl")
     test_args["num_classes"] = len(index2label)
 
     # load dev data
diff --git a/test/core/test_predictor.py b/test/core/test_predictor.py
index c7ad65d7..411f636e 100644
--- a/test/core/test_predictor.py
+++ b/test/core/test_predictor.py
@@ -4,6 +4,7 @@ import unittest
 from fastNLP.core.predictor import Predictor
 from fastNLP.core.preprocess import save_pickle
 from fastNLP.models.sequence_modeling import SeqLabeling
+from fastNLP.core.vocabulary import Vocabulary
 
 
 class TestPredictor(unittest.TestCase):
@@ -23,10 +24,14 @@ class TestPredictor(unittest.TestCase):
             ['a', 'b', 'c', 'd', '$'],
             ['!', 'b', 'c', 'd', 'e']
         ]
-        vocab = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, '!': 5, '@': 6, '#': 7, '$': 8, '?': 9}
+
+        vocab = Vocabulary()
+        vocab.word2idx = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, '!': 5, '@': 6, '#': 7, '$': 8, '?': 9}
+        class_vocab = Vocabulary()
+        class_vocab.word2idx = {"0":0, "1":1, "2":2, "3":3, "4":4}
 
         os.system("mkdir save")
-        save_pickle({0: "0", 1: "1", 2: "2", 3: "3", 4: "4"}, "./save/", "id2class.pkl")
+        save_pickle(class_vocab, "./save/", "class2id.pkl")
         save_pickle(vocab, "./save/", "word2id.pkl")
 
         model = SeqLabeling(model_args)
diff --git a/test/model/seq_labeling.py b/test/model/seq_labeling.py
index d7750b17..cd011c0d 100644
--- a/test/model/seq_labeling.py
+++ b/test/model/seq_labeling.py
@@ -38,7 +38,7 @@ def infer():
     # fetch dictionary size and number of labels from pickle files
     word2index = load_pickle(pickle_path, "word2id.pkl")
     test_args["vocab_size"] = len(word2index)
-    index2label = load_pickle(pickle_path, "id2class.pkl")
+    index2label = load_pickle(pickle_path, "class2id.pkl")
     test_args["num_classes"] = len(index2label)
 
     # Define the same model
diff --git a/test/model/test_cws.py b/test/model/test_cws.py
index 802d97ba..70716c3a 100644
--- a/test/model/test_cws.py
+++ b/test/model/test_cws.py
@@ -27,7 +27,7 @@ def infer():
     # fetch dictionary size and number of labels from pickle files
     word2index = load_pickle(pickle_path, "word2id.pkl")
     test_args["vocab_size"] = len(word2index)
-    index2label = load_pickle(pickle_path, "id2class.pkl")
+    index2label = load_pickle(pickle_path, "class2id.pkl")
     test_args["num_classes"] = len(index2label)
 
     # Define the same model