Abstract: Two different layout surge line models were established. Based on these two models, the thermal stratification was studied with numerical simulation using CFD respectively. Comparing the characteristics of thermal stratification between these two models under different mass flow rates, the reasons leading to different phenomena of thermal stratification for two models were analyzed. The results show that the location and range of thermal stratification are different due to different forms of fluid flow for two models. Meanwhile, the results can provide a reference for optimizing the surge line layout and weakening the thermal stratification effects.