Aiming at finding the solution to the problem of vibration and noise resulting from the torque fluctuation of a permanent magnet motor caused by cogging torque, auxiliary slots were used to reduce the cogging torque. The principle of suppressing cogging torque was analyzed and by changing the number, depth, width, slot area and slot shape of the auxiliary slot, Ansoft Maxwell software was used to model the permanent magnet motor, and the finite element method was used to analyze the effect of the auxiliary slot on cogging torque of the permanent magnet synchronous motor. Taking a 4-pole 36-slot motor as an example, the analysis results show that with two auxiliary rectangular slots whose depth, width and area are 0.7 mm, 1.2 mm, and 0.84 mm² respectively, the weakening effect is the most obvious, with the cogging torque 75.2% lower than that without an auxiliary slot. In addition, the back electromotive force changes little before and after the application of the auxiliary slot, and the amplitude of the fundamental wave of the air gap magnetic density decreases; the degree of 5th and 7th harmonic weakening is significant; the waveform distortion rate drops to 17.78%, and the motor performance is improved.