diff --git a/ppdet/data/reader.py b/ppdet/data/reader.py
index 3dce62d8eff338728b2e4e009308cb4b712327a6..cb5549892b94ce101cc1b78d5a9f422d5822446d 100644
--- a/ppdet/data/reader.py
+++ b/ppdet/data/reader.py
@@ -190,7 +190,7 @@ class Reader(object):
                  dataset=None,
                  sample_transforms=None,
                  batch_transforms=None,
-                 batch_size=None,
+                 batch_size=1,
                  shuffle=False,
                  drop_last=False,
                  drop_empty=True,