The liquid oxygen dynamic pressure sealing performance has a great influence on the working efficiency and stability of the liquid oxygen turbo pump.In order to study the phase transition and sealing performance of the mechanical seal liquid film under different working conditions,the end face liquid film vaporization phase transition numerical calculation model was established to analyze the degree of phase change of liquid film vaporization,the distribution of phase change region and the effect of liquid film vaporization phase change on the pump opening force and leakage.The results show that the working parameters have a certain degree of influence on the vaporization phase transition of the liquid film.With the increase of the moving ring speed and medium pressure,the phase transition is suppressed and the maximum phase transition volume fraction occurs at the pressure outlet and the range gradually decreases,the maximum phase transition pressure increases gradually,and the opening force and leakage increase continuously.The increase of medium temperature will promote the occurrence of phase transition,the maximum phase transition volume fraction occurs at the pressure outlet and the range gradually increases,the maximum phase transition pressure decreases continuously,and the opening force and leakage decrease continuously.The vapor phase transition of the liquid film have a direct impact on the sealing performance,and reasonable selection of sealing conditions can effectively utilize and control phase transition,so as to improve sealing performance.