Abstract: In order to adapt to the constructional features of the hydro pneumatic spring,the necessity of separate damping valve is proposed.Based on the 1/4 vehicle linear suspension model,the optimum damping coefficient is worked out and the parameters of the damping valve are determined with the(equivalent) linearization method.A structure of the damping valve is proposed so that it can fulfill the requirements of small size,high flowrate when the valve opens and the ability of enduring high back pressure.The damping valve had passed the bench test and worked properly.The method of design and the damping valve structure can be a useful guide in the design of hydro pneumatic suspension,especially in heavy duty vehicle design.