Abstract: In order to analyze and evaluate the effect of layout on the thermal stratification for PWR Pressurizer surge line,numerical simulation by Computational Fluid Dynamics（CFD） method is taken on 6 kinds of layout improvement with 2 improvement schemes,i.e.,increasing the obliquity of quasi horizontal section and adding a vertical pipe between the quasi horizontal section and next elbow,and the maximum temperature differences of quasi horizontal section of surge line of various layouts under different flowrate are obtained.The comparison shows that,the increasing of the obliquity of quasi horizontal section can mitigate the thermal stratification phenomena but can not eliminate this phenomena,while the adding of a vertical pipe between the quasi horizontal section and next elbow can effectively mitigate and eliminate the thermal stratification phenomena.