A numerical simulation is conducted to clarify the unsteady flow behavior and drag force around the oscillating flat plate immersed in MR fluids under the applied magnetic field. A modified Bingham model is adopted to take continuous viscous flow behavior at the very small shear rate and also magnetically variable yield stress into account. The measured yield stress is given to the model as a function of magnetic field intensity. The governing equations for the oscillating flat plate and unsteady MR fluids flow are derived by a modified Bingham model taking magnetic body force, yield stress and viscous force into account. The effects of magnetic field intensity, oscillation frequency and amplitude and further plate thickness on the fluid flow and damping characteristics around the oscillating flat plate are clarified by the numerical simulation.