The sketch of hydro-pneumatic spring was shown, the superposition throttle slices and the adjustment gasket were studied, the stress computation formula of superposition throttle slices and the thickness design formula of adjustment gasket were established. With the velocity and the pressure of opening valve of hydro-pneumatic spring, throttle aperture design formula of hydro-pneumatic was built, the affection of superposition throttle slices and adjustment gasket thickness on the throttle aperture was analyzed. With the practical example of hydro-pneumatic spring, the superposition throttle slices, the adjustment gasket and the throttle aperture were designed, the equivalent thickness, opening valve characteristic and stress intensity were validated, and the performance test was conducted for the designed hydro-pneumatic spring. The experimental and analytic results show that the methods of throttle aperture design for hydro-pneumatic spring is reliable, which has important reference value for hydro-pneumatic spring design.