As a controllable damper, magnetorheological(MR) damper can play an important role in the vibration control system, especially as a semi-active control device. In this paper, an experimental setup has been made for investigating the characteristic of MR damper and analyzing its vibration isolation characteristics. The analytical model that consists of a hysteresis part and a variable viscous damper proportional to the added voltage is used to describe the performance of a MR damper. Two on-off damper control policies based on the product of relative velocity and relative displacement are proposed. The numerical simulation and experiment are performed to investigate the effects of the two kinds of on-off dampers and conventional on-off damper in the single-degree-of-freedom system. The results show that on-off dampers express the better vibration performance than the uncontrolled MR damper, two proposed on-off dampers have the better vibration performance in the high frequency domian than that of conventional on-off damper, and the controllable MR damper is very effective for vibration control.