Abstract: A half-car active suspension system model with four degrees of freedom is established and a strictly(Q,S,R)-dissipative state feedback controller is designed based on the dissipative system theory.The system based on Matlab/Simulink environment is simulated and four performance indexes such as body acceleration,pitch angle acceleration,suspension dynamic travel and tire dynamic deflection are compared between the active and passive suspensions.The simulation is achieved by the method of time domain and frequency domain.Resultsshow that,the riding comfort performance and smoothness of traveling movement of the vehicle are evidently improved by using the active suspension with a strictly dissipative controller.