Although the sensorless strategy has been widely used in general industrial occasions, it has not been applied in the field of position servo. The reason is that the rotor mechanical angle cannot be identified. Therefore, a sensorless identification strategy of surface permanent magnet synehromous motor (SPMSM) rotor mechanical angle with auxiliary teeth based on high-frequency voltage injection is proposed. According to the mathematical model of SPMSM with auxiliary teeth, the mechanical sector is divided by injecting high-frequency voltage signal at the electrical angle zero point. The traditional sensorless algorithm is used to obtain the electrical angle. Finally, the mechanical angle is obtained from the relationship among electrical angle, mechanical sector and mechanical angle. The simulation results show that the proposed algorithm can identify the mechanical angle of the motor rotor.