Abstract: A 7-DOF nonlinear full vehicle model with semi-active hydro-pneumatic suspension was established. Aiming to improve the ride comfort ability, a sliding mode controller with sky-hook reference model was designed based on the nonlinear full vehicle model. The damping force on each suspension unit was controlled individually by the controller so that the responses of the controlled vehicle could follow those of the reference model. The performance of the designed controller was validated in the Matlab simulation environment. The simulated vehicle was subjected to a class-D road profile at 54 km/h. Simulation results show that, compared with passive suspension, the sliding model controller can effectively decrease the vertical, pitch and roll vibration of the sprung mass. The model reference sliding mode control has a strong robustness on road disturbance and parameter variety, and it is eligible for the nonlinear hydro-pneumatic suspension control.