The installation angle of hydropneumatic suspension cylinders has important influence on the stiffness characteristics of the interconnected hydro-pneumatic suspension system. Based on the installation angle of hydropneumatic suspension cylinders, the theoretical stiffness calculation formula of the interconnected hydropneumatic suspension system was deduced and its model was established by MATLAB software. The ADAMS and AMESim software were used to establish the corresponding cosimulation validation model, and an experimental test platform was built. The theoretical calculation, simulation and experimental tests of roll stiffness and vertical stiffness were carried out for the interconnected hydropneumatic suspension system. The comparison of the results from the theoretical calculation, simulation and experiment indicates that they had high consistency. It was verified the correctness of the theoretical formula. Moreover, the characteristics of the roll stiffness and vertical stiffness of different installation angles of hydropneumatic suspension cylinders were analyzed.The analysis results show that with the increasing of the installation angle of hydropneumatic suspension cylinders, the tendency of the roll stiffness of the suspension decreases,nonlinear characteristics of roll stiffness become weaker,and the vertical stiffness of the interconnected hydropneumatic suspension increases.