Abstract: To study the pressure pulsation characteristics of the cryogenic expander, the numerical simulation was performed on the expander hydraulic model by the numerical simulation method. Firstly, external characteristics of expander were obtained by steady numerical simulation. Simulation results were compared with test results, verifying the accuracy of simulation results. The unsteady numerical simulation was performed based on the results of steady numerical simulation.The time-domain plot at different monitoring points of the guide vane and the runner was drawn, and the frequency-domain plot at monitoring points was obtained through fast Fourier transform. The results show that the effect of dominant frequency at the monitoring point of the runner on fluid is as consistent as that of the number of the guide vanes and the effect of dominant frequency at the monitoring point of the guide vanes on fluid is as consistent as that of the number of the runner. The amplitude of the dominant frequency at the monitoring point is related to the point location. When the monitoring point is close to the vaneless area between the guide vane and the runner, the amplitude is larger. The further the distance from the vaneless area is, the smaller the amplitude is, and the smaller the influence of dynamic and static interference between the guide vane and the runner is. The research could provide reference for the design of cryogenic expander.