Semi-active suspensions based on magnetorheological (MR) dampers are expected to innovate automotive suspension systems. However, the accuracy of the damping force models of MR dampers affects the control performance of MR semiactive suspension systems. Based on the experimental data of a self-developed MR damper, the parameters of a resistorcapacitor (RC) hysteresis model are identified. The obtained RC hysteresis model can describe and predict the hysteresis nonlinear damping force of the MR damper effectively. Further, the dynamic model of a 1/4 MR semi-active suspension system based on the MR damper is established, and a linear quadratic regulator (LQR) control strategy based on state feedback is designed. The performance of the 1/4 MR semi-active suspension system is simulated and analyzed in time and frequency domains.