Abstract: The gas separator is a key device in the gas removal system for molten salt reactor. It removes the fission gases contained in the carrier gas by a centrifugal process. In this paper, CFD software Fluent was used to investigate the performance of a gas separator under different conditions by using the transient turbulence model of quadratic pressure-strain RSM. The results show that the outlet pressure has a relatively significant effect on the distributions of velocity and pressure, and consequently influences the separation process. The enveloping surface of zero axial velocity was obtained, further indicating that the increase of the outlet pressure is beneficial to the separation.