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A research method of modeling hydro-pneumatic spring mechanical characteristic was presented. According to the calculation method of the sectional linear speed characteristic, the structural parameters of damping valve at the valve open point and the maximal valve open point, such as aperture width, predeformation of slice and positive retainer ring, were designed respectively by using sheet mechanics theory and fluid mechanics theory. The elastic force of hydro-pneumatic spring was deduced by the modified perfect gas equation. The correctness of the design method was validated through the comparison between performance test and simulation data. Eventually, the influence rules of different cylinder bodies and physical parameters on the speed characteristic of hydro-pneumatic spring were programmed and analyzed so as to provide reference for the research on the internal characteristic of damping equipment. 