diff --git a/docs/chapter5/chapter5.md b/docs/chapter5/chapter5.md
index 1e70b47..eb4176d 100644
--- a/docs/chapter5/chapter5.md
+++ b/docs/chapter5/chapter5.md
@@ -264,4 +264,7 @@ $$
 ## References
 
 * [OpenAI Spinning Up ](https://spinningup.openai.com/en/latest/spinningup/rl_intro.html#)
+* [百面机器学习](https://book.douban.com/subject/30285146/)
+
+