Abstract: Ideal power-train mounting systems should have large stiffness and damping at low frequencies and large amplitudes, small stiffness and damping at high frequencies and small amplitudes. To solve the problems of small controllable range of dynamic stiffness, large field-off dynamic stiffness and limit stroke of the existing magneto rheological (MR) fluid mounts, a MR fluid mount with an inner bypass valve was proposed and developed. The MR fluid mount was designed to provide a wide range of dynamic stiffness in full working frequency range, small field-off dynamic stiffness and maximum stroke. Electromagnetic field simulation analysis of the MR fluid mount was carried out with a finite element simulation software. A mathematical model of the MR fluid mount was built. Experimental tests based on the servo-hydraulic test system were conducted.