In order to solve the problem that the character of magnetoreological fluid damper based on squeeze mode is not suitable for the vehicle because of large damping force and small displacement, the ball-screw outer structure of a damper is designed, and the mechanical and dynamic models are established. The influence of the external connecting rod velocity, displacement and the magnetoreological fluid flow shear yield strength on the damping force is calculated and simulated. Both the indication and the effect of the connection rod length on the regulation mode of the damper are also analyzed. A bench test is carried out in the end, and the indicator diagrams under different current are obtained which is close to the theoretical result. The results demonstrate that the deduced mechanical model is effective, and that the ball screw structure can increase the adjustable range of displacement and damping force, making it suitable for the vehicle. In addition, the damper with this structure possesses mechanical electromagnetic dual regulation mode.