The magnetic field modulated variable speed permanent magnet brushless motor (MFMVS-PMBM) is a new type of power shunting device for hybrid electric vehicles (HEVs), which is composed of magnetic gear and permanent magnet brushless motor. Compared with the conventional double rotor motor, the MFMVS-PMBM shows a more complex electromechanical energy conversion relationship due to its special magnetic field modulation principle. In order to obtain better electromagnetic characteristics of the motor, the key parameters of magnetic gear and permanent magnet brushless motor are optimized in this study. The effects of gear ratio, the number of blocks per pole of Halbach array and the angle of connecting bridge and magnetic isolation bridge on the torque of magnetic gear are analyzed. The electromagnetic characteristics of the motor, such as pole slot matching, permanent magnet thickness and slot opening width of permanent magnet brushless motor, are also analyzed. Finally, the prototype is made and the experimental platform is built. The results show that MFMVS-PMBM has good sinusoidal back electromotive force (EMF), high transmission efficiency and power factor.