Abstract: The sealing performance of the space station is of vital importance in ensuring the normal operation of the station. In this paper, the physical model of the molecular movement in the vacuum environment is established to analyze the potential ammonia leakage which may take place during the operation of the space station. The DSMC method is used for numerically simulating the process of the gas leaking into the space. The number density distribution data of the plume field under different conditions are obtained, to provide a theoretical basis for the subsequent experiments.