diff --git a/fastNLP/core/callback.py b/fastNLP/core/callback.py
index 9dce426b..7f5624d8 100644
--- a/fastNLP/core/callback.py
+++ b/fastNLP/core/callback.py
@@ -168,7 +168,7 @@ class Callback(object):
         :param dict batch_x: DataSet中被设置为input的field的batch。
         :param dict batch_y: DataSet中被设置为target的field的batch。
         :param list(int) indices: 这次采样使用到的indices，可以通过DataSet[indices]获取出这个batch采出的Instance，在一些
-            情况下可以帮助定位是哪个Sample导致了错误。
+            情况下可以帮助定位是哪个Sample导致了错误。仅在Trainer的prefetch为False时可用。
         :return:
         """
         pass
diff --git a/fastNLP/core/dataset.py b/fastNLP/core/dataset.py
index b506dfae..38623caa 100644
--- a/fastNLP/core/dataset.py
+++ b/fastNLP/core/dataset.py
@@ -365,6 +365,15 @@ class DataSet(object):
             if idx not in self:
                 raise KeyError("No such field called {} in DataSet.".format(idx))
             return self.field_arrays[idx]
+        elif isinstance(idx, list):
+            dataset = DataSet()
+            for i in idx:
+                assert isinstance(i, int), "Only int index allowed."
+                instance = self[i]
+                dataset.append(instance)
+            for field_name, field in self.field_arrays.items():
+                dataset.field_arrays[field_name].to(field)
+            return dataset
         else:
             raise KeyError("Unrecognized type {} for idx in __getitem__ method".format(type(idx)))