A new control method used in the semi-active suspension is studied. The force generated by the semi-active damper can be divided into two parts, one is the uncontrollable force, and the other is the controllable force. In order to make the sprung mass have the ideal isolation effect, the controllable force should be equal to the sum of the uncontrollable force and the force generated by the suspension spring. But the controllable force is limited by many constraints. Therefore, the control strategy can be concluded. The simulation results show that the ride comfort and handling stability are both improved by the control method.