Abstract: Aiming to the problem of poor performance of tractor vibration, a flow pattern was developed on the basis of a damping force mathematical model, which was presented with analyzing working pattern of the magnetorheological damper(MRD). According to working requirements of large wheel tractor front axle suspension, a single outstretch pole MRD was designed. Experiments were conducted to assess the impact of input current and the excitation rate on the shock absorber damping force. It is observed that the damping force controllable ratio reaches 5.9 in low speed situation. Whereas, it increases with the applied current to its peak value of 1.8 A and the maximum output damping force reaches at 1 370 N. Perceived results justify the validity of the design, and provide the evidence for controlling semi-active air suspension with adjustable damping.