diff --git a/paddle/fluid/operators/lrn_mkldnn_op.cc b/paddle/fluid/operators/lrn_mkldnn_op.cc
index 692933405b830e723e2e83a6c07e19ec6bd5432d..097ba01d401dbc7969e30f576cac2567c874ed99 100644
--- a/paddle/fluid/operators/lrn_mkldnn_op.cc
+++ b/paddle/fluid/operators/lrn_mkldnn_op.cc
@@ -67,6 +67,12 @@ class LRNMKLDNNOpKernel : public paddle::framework::OpKernel<T> {
     mid->mutable_data<T>(ctx.GetPlace());
 
     const int n = ctx.Attr<int>("n");
+    // MKL-DNN implements LRN in a caffe way:
+    // http://caffe.berkeleyvision.org/tutorial/layers/lrn.html
+    // Where sum of squares is divided by size of normalization window
+    // this is not the case for PaddlePaddle LRN.
+    // Hence we need to compensate for this diffrence by
+    // multipliing alpha by size of window(n)
     const float alpha = ctx.Attr<float>("alpha") * static_cast<float>(n);
     const float beta = ctx.Attr<float>("beta");
     const float k = ctx.Attr<float>("k");