Abstract: In order to analyze and evaluate the effect of pipe type on thermal stratification for PWR pressurizer surge line, computational fluid dynamics (CFD) method was used for the current and improved screw surge line during heating up condition. The maximum temperature differences and velocity distribution along the surge line axis under different velocities were obtained. Comparative analysis indicates that replacing current smooth tube with screw pipe can enhance the turbulent flow and the mixing effects between the hot and cold fluids. The temperature differences in flow cross sections along the screw surge line axis are reduced by about 1/3 compared with current smooth surge line, yielding effectively mitigation to the influence of thermal stratification.