Ride comfort and handing stability are the two important driving features of vehicle. In the process of suspension design, ride comfort and handing stability are two conflicting considerations. Magneto-rheological(MR) fluid dampers are a new class of devices that more suitable for the requirements of automotive applications, including having very low power requirements. According to different driving conditions and body posture, semi-active suspension based on MR damper can coordinate the body posture angle, and reduce the vibration from suspension pass to vehicle body. This paper deals with theoretical analysis and experiments of MR fluid damper in semi-active suspension system. Based on a large number of experimental data, a mathematical MR damper model was adopted to predict both the force-displacement behavior and the complex nonlinear force-velocity response. For the purpose of developing semi-active controller, a detailed vehicle Virtual Prototyping model with steering, frame and semi-active suspensions systems was established by vehicle dynamics simulation software SIMPACK. The co-simulation of ride comfort and handing stability showed that the semi-active suspension designed in this paper was suitable for solving the conflict between ride comfort and handing stability, and improve the ride and handing performance simultaneously.