A kind of hydro-pneumatic suspension with controllable damping was designed. A complex nonlinear mathematic damping model of hydro-pneumatic suspensions was set up on the basis of comprehensive analysis of its working principle and structure. The effects of the controllable valve structural parameters on the hydro-pneumatic suspension damping characteristics were mainly discussed by using software Matlab/Simulink. The comparison of simulation results and bench test showed that the mathematic model is authentic, and the perfect damping characteristics of the hydro-pneumatic suspension could be obtained through rational selection of the valve structural parameters, such as the size of the parallel or series orifices, the maximum opening capacity or the spring pre-compression of the one-way valve.