The hydro -pneumatic suspension with its good non -linear characteristic is widely used. The single chamber hydro -pneumatic suspension system is used as the research object. By considering the dissolution and mixing of gas in oil, mixed oil compressibility and friction force of the internal sealing, based on the equation of state of gas, oil orifice flow equation, its non -linear mathematical model was established, which was used to identify the main structural parameters and operate parameters which affected the output characteristics of the suspension. The hydro -pneumatic suspension test bench was design and built, and the virtual prototype model was built in ADAMS, hydraulic system model of the hydro -pneumatic suspension was built in AEMSim, the weighted function frequency filter was designed and built in Simulink, and the combined model was built based on ADAMS/AMESim/Simulink models. Through the test and simulation results compared, the accuracy of the model is verified; the effect of main parameters on the dynamic characteristics is analyzed, which provides reference for practical design.