Based on equivalent root mean square （RMS） of structural deflection criteria

a simplified model is established for MR damper used in passive control. The mechanical performance of MR dampers is related to applied voltage

displacement amplitude and frequency. The equivalent viscous damping coefficient （EVDC） and the equivalent stiffiness coefficient （ESC） capture the salient features of MR dampers. EVDC has larger variation when applied voltage is in the range of 0 V to 5 V and it come to saturation with voltage reach 10 V. When MR damper applied voltage vibrates in the region of lower frequency and small amplitude

stable EVDC is obtatined. When voltage is equal to 0 V EVDC decreased rapidly with the increase of frequency and amplitude. The transformation of MR damper mainly concentrates on the region of higher frequency and larger amplitude. The size of ESC is about 0.1 time that of EVDC and the factors influence upon ESC is discussed.