Abstract: A sliding mode controller for semi-active suspension system of a quarter car is designed with sliding model varying structure control method.The skyhook is chosen as a reference model for this controller to force the tracking error dynamics between the reference model and the plant in an asymptotically stable sliding mode.An equal near rate is used to improve the dynamic quality of sliding mode motion.Simulation result shows that the stability of performance of the sliding-mode controller can effectively ensure the driving smoothness and safety.