Adopting a pressure-maintaining storage system in a wave power station is a new idea for converting the unsteady ocean wave energy input into the steady power output. According to the idea， the implemented system consists of an energy input system， a hydraulic pressure system， a generating system and a control system. In this paper， a mathematical model of the system is established and the computer simulation is done according to the mathematical model. Based on the physical mode， the unsteady wave energy input is simulated by the way of the motor driven by a transducer and the differential PID control algorithm is applied to the control system. The computer and physical mode simulation results show that the system can convert the unsteady energy input into the steady electric energy output. The idea is feasible and valuable for the design of actual systems.