Aiming at a serial combined resistance element,the numerical simulation of the unsteady flow caused by the movement of the spool was carried out based on dynamic mesh and the 6 DOF solver.The internal flow field changes caused by spool movement were discussed and the outlet pressure pulsation characteristics of the combined hydraulic resistance element were analyzed.The effects of spool movement on pressure field and velocity field were studied.The results show that with the rising of the spool movement,there are two obvious vortex areas in the cavity between the fixed damping hole of the combined hydraulic resistance element and the adjustable throttle orifice,which disappear with the increase of the valve orifice opening;when the spool makes the attenuated oscillation to the steady status,the two vortex areas reappear and exist eternally.The oscillation attenuation movement of the spool makes the internal flow rate and pressure produce similar oscillation motion fluctuations,and the outlet pressure and flow rate will also fluctuate first and then reach steady state as the spool reaches steady state.