Permanent magnet synchronous motors have been widely used in various fields due to their high power density, efficiency, and reliability. In applications that require mechanical angles, position sensors are generally used to obtain the mechanical position information of the motor rotor, which can reduce the reliability, integration, and power density of the control system. In order to achieve mechanical angle identification of permanent magnet motors without the use of position sensors, the electromagnetism of a surface-mounted permanent magnet synchronous motor (SPMSM) is designed. By adding auxiliary teeth of different heights to the rotor, the inductance of the motor topology includes the mechanical angle information of the rotor. The negative effects of adding auxiliary teeth on the back electromotive force, output torque, and three-phase inductance of the motor are analyzed using finite element simulation software. Finally, the mechanical angle identification ability of the proposed topology is verified on the 0.75 kW SPMSM platform.