Abstract: To solve the problems of vehicle body attitude change and vertical vibration due to vehicle driving conditions and uneven road surface, a control method for vehicle semi-active suspension was designed based on magnetorheological semi-active suspension system, which was composed of attitude compensation control algorithm, magnetorheological damper control algorithm and accurate state observer design method. The vehicle attitude control and the suspension vertical vibration control were considered in the attitude compensation control algorithm, and the equivalent damping control of the magnetorheological semi-active suspension system was carried out by the magnetorheological damper control algorithm to optimize the body attitude and improve the vehicle comfort. To estimate the required speed signals more accurately, the actual equivalent damping was used to update the parameter matrices in the observer in real time, and the accurate state observer was constructed. The simulation and experimental results show that body acceleration, pitch angle acceleration and roll angle acceleration can be improved effectively by the proposed control algorithm, and RMS values of them are respectively reduced by 14.03%, 18.26% and 21.39%, which implies the effectiveness of the designed control algorithm.