The 550kV high voltage circuit breaker with hydraulic operating mechanism is t aken as the investigation subject. The pressure loss in pipe and the pressure wa ve propagation in the process of opening and closing motion are analyzed. The mo del of the pressure loss in pipe and the model of the pressure wave distributed parameter are established. Simulation is carried out by using AMEsim software. The inf luence of the pipe characteristics and structure parameters on the system perfor mance is discussed. The simulation results are thought to be in accordance with the experiment results. It shows that the models are correct.