The invention discloses a magneto-rheological damper capable of improving damping force and failure safety. The magneto-rheological damper is mainly composed of a piston rod, a damper end cover, a piston head end cover, a magnetic conducting outer sleeve, a damper cylinder body, a non-magnetic conducting dividing ring, excitation coils, magnetic conducting rods, a magnetic conducting inner sleeveand the like. External vibration enables a combined piston and the damper cylinder body to move relatively, the four magnetic conducting rods and the four excitation coils which are perpendicular to each other form a unique magnetic field polarization arrangement mode, and polarization of each magnetic pole is opposite to that of the adjacent magnetic pole. The most surface area of a liquid flow channel is covered with a magnetic field in an orthogonal mode so that the active area of magneto-rheological fluid can be enlarged, and output damping force is improved. At the same time, the four excitation coils are adopted, and when one certain excitation coil is damaged or fails to work, the other excitation coils can still be used normally, and the failure of the controllable output damping force is avoided. The magneto-rheological damper is particularly suitable for being applied to a magneto-rheological damper semi-active damping system.