Abstract: The importance of stufying damping valve water hammer pressure was presented because a damping valve with hydro-pneumatic spring was stroked frequently when a vehicle ran on off road. The transferring rules of water hammer wave near a valve were analyzed after the physical model of a damping valve was built. The method of latent lines and the oil route boundary conditions were used to solve the partial differential equations of water hammer. The mathematic model of the whole damping valve, with a throttle orifice was established after the theory of water hammer was applied to miniature hydraulic pressure devices successfully. The influencing rules of the throttle orifice position and the structural parameters on the damping valve reliability were studied. The analysis reults showed that the throttle orifice should be set near the valve, and the larger the sige if the throttle orifice, the less the oscillation time of water hammer, the smaller water hammer pressure on the valve; these results can offer a reference for designing a damping valve.