Abstract: With the rheological property of magnetorheological (MR) fluids in the presence of applied magnetic field and in the different shear strain rate as well as the mechanical principium of MR damper in the mix mode, a simplified mechanical model with four indeterminate coefficients is developed. Based on the testing datum of damping force and velocity of piston rod as well as exciting current of MR damper coil by MTS8701 system, the coefficients of the model are determined. Let the dynamic-response time of voltage driver and MR damper electromagnet system add to the change time of catenulate-state, utilized as time-delay factor of the dynamic performance of MR damper, the simplified mechanical model can be established. The test and simulation result show that the simplified mechanical model can be use to describe the basic mechanical behavior of MR damper.