diff --git a/docs/system.rst b/docs/system.rst
index 75aaf62..5e0c679 100644
--- a/docs/system.rst
+++ b/docs/system.rst
@@ -193,3 +193,8 @@ Utils for handling system, like to track file, make directory, link and so on.
     >>>
 
     .. note:: ``chcp`` can only be used on ``Windows`` system.
+
+
+.. py:function:: pydu.system.preferredencoding(code)
+
+    Get best encoding for the system.