To address the finishing difficulties of existing medical titanium alloy bone screws， such as complex structure， different sizes， and surface burrs， a new finishing method known as drum type ultrasonic magnetorheological compound finishing was proposed， and a drum-type ultrasonic magnetorheological compound finishing device was designed independently. The device adopts an electromagnetic excitation mode with a three-magnetic pole excitation structure. The structural size and coil parameters of the excitation device are determined by theoretical calculations and a Maxwell simulation analysis. A roller-type ultrasonic–magnetorheological compound finishing experimental platform is built. An excitation current single-factor polishing experiment is performed. The magnetic induction intensity of the MR fluid in the finishing device is measured and compared with the simulation results. When the width of the n-pole of the electromagnetic excitation device is 35 mm， the number of turns of the coil is 1 080， and the wire diameter is 1.25 mm， the maximum current that can pass through the coil is 5 A. Moreover， the finishing area can form a good magnetic circuit， the magnetic field distribution can form the magnetorheological and abrasive finishing areas， and the magnetic induction intensity of the magnetorheological finishing area can reach up to 0.57 T. The magnetic induction intensity of the MR fluid in the finishing area of the drum is less than the simulation value. The surface roughness change rate of the workpiece before and after polishing increases first and then decreases with an increase in the excitation current. When the current is 4 A， the surface roughness decreases from 1.39 μm to 0.435 μm， and the maximum surface roughness change rate is 68.7%. The magnetic induction intensity of the electromagnetic excitation device with a three-pole excitation structure can meet the requirements of the magnetic field in the finishing of MR fluids， and the effective polishing area is large.