In order to verify the nonlinear characteristics of the hydraulic cylinder and accumulator, the hydraulic system of crane hydropneumatic suspension was studied as the object of study. The mathematical model of stiffness for hydropneumatic suspension system was established and some stiffness curves were made with the help of MATLAB.Stiffness characteristics under different experimental conditions were analyzed and compared . The gap between theoretical model and experimental results was pointed out.The stiffness variation trend of hydropneumatic suspension system is verified,which provides reference significance for other performance analysis of hydropneumatic suspension system.