Cushion structure of high-speed cylinder of the 550kV high voltage circuit breakers was analyzed. The flow characteristics of the cushion structure were estimated by Reynolds number and a simulation model was built with the results of CFD analysis. Pressure, velocity and displacement characteristics of the cylinder were simulated. The simulation results and the test results were compared. It indicated that the simulation method was effective and the simulation model was accurate. Dynamic characteristics of the cushion process of high speed hydraulic cylinder were revealed, and reasons for high peak pressure and high end-velocity were pointed out. The proposed method could help the optimization of cushion structure. 