diff --git a/source/conf.py b/source/conf.py
index e8046e3..4c1cbf0 100644
--- a/source/conf.py
+++ b/source/conf.py
@@ -199,6 +199,7 @@ latex_elements = {
 \setCJKmonofont{SimHei}
 \XeTeXlinebreaklocale "zh"
 \XeTeXlinebreakskip = 0pt plus 1pt
+\setcounter{tocdepth}{3}
 ''',
 }
 
diff --git a/source/index.rst b/source/index.rst
index 476ab47..8326388 100644
--- a/source/index.rst
+++ b/source/index.rst
@@ -9,7 +9,7 @@
 Contents:
 
 .. toctree::
-   :maxdepth: 2
+   :maxdepth: 3
 
    overview
    introduction