diff --git a/python/paddle/v2/fluid/layers/nn.py b/python/paddle/v2/fluid/layers/nn.py
index a79479f469a0c489edf2676bc5d07066bb480664..fe6d87e5d7c33d434a4379bb40c7ca24767f258a 100644
--- a/python/paddle/v2/fluid/layers/nn.py
+++ b/python/paddle/v2/fluid/layers/nn.py
@@ -92,7 +92,7 @@ def fc(input,
 
     .. math::
 
-        Out = Act({\sum_{i=0}^{N-1}W_iX_i + b})
+        Out = Act({\sum_{i=0}^{N-1}X_iW_i + b})
 
     In the above equation: