diff --git a/fastNLP/core/dataloaders/utils.py b/fastNLP/core/dataloaders/utils.py
index 06f09da3..4f8fa743 100644
--- a/fastNLP/core/dataloaders/utils.py
+++ b/fastNLP/core/dataloaders/utils.py
@@ -118,17 +118,22 @@ class OverfitDataLoader:
     实现一个简单的迭代器来模拟实际的 dataloader，从给定的 dataloader 中取出部分数据，来让 Trainer 实现 overfit 的功能；
     """
 
-    def __init__(self, dataloader, overfit_batches: int):
+    def __init__(self, dataloader, overfit_batches: int, batches=None):
+        # batches 参数是给重新初始化dataloader使用的
         self.dataloader = dataloader  # 需要将实际的 dataloader 挂载到该对象上，从而应付一些对于实际的 dataloader 的操作；
-        self.batches = []
-        self.overfit_batches = int(overfit_batches)
-
-        if self.overfit_batches > len(dataloader):
-            logger.warning("Parameter 'overfit_batches' is bigger than the length of 'train_dataloader'.")
-
-        for idx, batch in enumerate(dataloader):
-            if idx < self.overfit_batches or self.overfit_batches <= -1:
-                self.batches.append(batch)
+        if batches is None:
+            self.batches = []
+            self.overfit_batches = int(overfit_batches)
+
+            if self.overfit_batches > len(dataloader):
+                logger.warning("Parameter 'overfit_batches' is bigger than the length of 'train_dataloader'.")
+
+            for idx, batch in enumerate(dataloader):
+                if idx < self.overfit_batches or self.overfit_batches <= -1:
+                    self.batches.append(batch)
+        else:
+            assert isinstance(batches, list)
+            self.batches = batches
 
     def __len__(self):
         return len(self.batches)
diff --git a/fastNLP/core/dataset/dataset.py b/fastNLP/core/dataset/dataset.py
index fff8b5c2..0238a65d 100644
--- a/fastNLP/core/dataset/dataset.py
+++ b/fastNLP/core/dataset/dataset.py
@@ -445,7 +445,7 @@ class DataSet:
                     "DataSet object has {} fields, but attempt to append an Instance object with {} fields."
                         .format(len(self.field_arrays), len(instance.fields)))
             for name, field in instance.items():
-                assert name in self.field_arrays
+                assert name in self.field_arrays, f'Field:`{name}` is not found in {self.field_arrays.keys()}'
                 try:
                     self.field_arrays[name].append(field)
                 except Exception as e: