diff --git a/tools/diff_api.py b/tools/diff_api.py
index ec51711d68a155dabdf3125d43fc35bab0b0c944..fe6a2aa819fd4151685d6a9b8ace193975ea9e59 100644
--- a/tools/diff_api.py
+++ b/tools/diff_api.py
@@ -30,6 +30,6 @@ if error:
         '''If you modify/add/delete the API files, including code and comment, please follow these steps in order to pass the CI:
     1. cd ${paddle_path}, compile paddle;
     2. pip install build/python/dist/(build whl package);
-    3. run "python tools/print_signatures.py paddle.fluid, paddle.reader > paddle/fluid/API.spec"'''
+    3. run "python tools/print_signatures.py paddle.fluid,paddle.reader > paddle/fluid/API.spec"'''
     )
     sys.exit(1)