The invention discloses a rotary ultrasonic magneto-rheological brush polisher. The rotary ultrasonic magneto-rheological brush polisher comprises a base plate, a magneto-rheological brush device, a rotary ultrasonic system and a motor, wherein the motor is used for driving the magneto-rheological brush device to rotate by virtue of the rotary ultrasonic system; the rotary ultrasonic system comprises an outer shell, an inner shell and an energy converter; the energy converter is arranged inside the inner shell and is connected with an amplitude-change pole; the amplitude-change pole is connected with the magneto-rheological brush device; a rolling bearing is arranged between the inner shell and the outer shell; and the outer shell is fixedly arranged on the base plate. The rotary ultrasonic magneto-rheological brush polisher disclosed by the invention has the advantages that the structure is simple, the rotary ultrasonic system is additionally arranged in running of the magneto-rheological brush device, and the inner shell and the amplitude-change pole of the rotary ultrasonic system are used for transmitting torque and also generating ultrasonic wave, so the polishing effect and the polishing efficiency are greatly improved.