The influence of check valve on the output performance of the PZT hydraulic pump was analyzed, especially its natural frequency. The fluid structure interaction (FSI) analysis, which effect of liquid added mass, added damping and the solid wall on the natural frequency of the check valve have been taken into account, is presented. Besides, an experiment was set up to validate the flow rate result. The obtained results reflect that the gap height between check valve and a solid surface has a major impact on check valve’s natural frequency in liquid. The flow rate value and optimal frequency of the PZT pump can be improved by the design of the check valve.