In our recent work, we have proposed a novel force control actuator system called series damper actuator (SDA). We have since built an SDA system based on magneto-rheological fluid (MR) damper. In this paper, the dynamics property of SDA system based on the MR fluid damper (SMRDA) is investigated. The effect of the extra dynamics introduced by the MR fluid damper is revealed by comparing the SMRDA with the SDA system based on a linear Newtonian viscous damper (SNVDA). To linearize the constitutive property of the MR fluid damper, a modified Bingham model is proposed. A force feedback control loop is implemented after the linearization. An experimental SMRDA is built to illustrate the performance of the SDA system.