Using Bingham fluid model, the braking torque of the magnetorheological fluid disc brake was studied, and a single disc brake structure with outer winding coil was designed. COMSOL software was used to model the structure, simulate the electromagnetic field, calculate the braking torque and optimize the structural parameters. The research shows that the brake torque has nothing to do with the angular velocity of the shear disc, and the brake can obtain a relatively stable brake torque during the braking process. Under certain magnetomotive force, when the radius of shear disc increases, the braking torque of disc brake will increase gradually. Increasing the thickness of the magnetic-conducting shell is beneficial to restrain the magnetic field line and improve the braking torque.