There are many nonlinear factors in the model of hydropneumatic suspension system in engineering vehicles. According to its structure properties and the working principal, the nonlinear mathematical model was set up upon the IdealGas equation and oil small orifice flow equation. On this basis, mathematical model was built by Simulink, and hydropneumatic suspension system test bench multibody dynamics model was built by ADAMS. In order to verify the accuracy of the model, the dynamic characteristics test of hydropneumatic suspension struts was conducted. The influence law of the excitation frequency change to the dynamic characteristics of hydropneumatic suspension struts was obtained. The accuracy and reliability of the nonlinear mathematical model and ADAMS multibody dynamics model of hydropneumatic suspension are verified by analysis with comparison of results from cosimulation and experiments, which provide an important reference for research in characteristics of engineering vehicle dynamics and hydropneumatic suspension system.