Abstract: The cogging torque of a spoke-type permanent magnet(PM) motor increases the torque ripple of the motor, which affects the reliable operation of the spoke-type PM fault-tolerant servo motor and the control accuracy of the whole control system. To decrease the cogging torque and improve the control accuracy of the motor, firstly, the relationship between cogging torque and slot-pole combination, as well as the principle of cogging torque generation, are analyzed based on the energy method. Then, the effects of the two methods of opening auxiliary slots in the stator and opening auxiliary slots in the rotor on the cogging torque of PM motors are discussed. The results show that adding irregular auxiliary slots at both ends of the spoke PMs helps to minimize the cogging torque. The main reason is that adding auxiliary slots can change the direction of the rotor flux path, and the appropriate auxiliary slots can be selected according to the flux path. In addition, it increases the fundamental amplitude and decreases the harmonic component of the air-gap density, thus improving motor performance. The cogging torque of the proposed motor is 4.1 mN·m and the torque ripple is 0.16%. Cogging torque and torque ripple are optimized to meet the high precision and stability requirements of servo motors. Finally, a 24-slot/22-pole prototype motor with irregular auxiliary slots on the rotor is fabricated and tested, and the corresponding experiments verify the proposed method’s effectiveness.