Abstract: The engine of cryogenic liquid rocket is required for fully precooling by natural circulation before launching,and the return flow location of the circulation loop plays an important part in field distribution of tank.In the present investigation,the physical field of tank with different return flow locations was simulated numerically based on computational fluid dynamics(CFD) technique,the distributions of temperature and velocity fields were depicted,the effect of the return flow location on thermal stratification was analyzed.It is found that the return location at 2 meter above the bottom header is optimal,where the volume and depth of subcooled liquid oxygen in tank have the most values,thus providing an important theoretical support to the design of rocket propulsion system.