The cogging torque of the interior permanent magnet synchronous motor brought a series of problems such as torque ripple, motor control accuracy deterioration, vibration and noise, so it was important to take effective measures to weaken the cogging torque. The influence of radial segmenting of permanent magnet on cogging torque was analyzed by analytic calculation. Based on this, an improved segmenting method of permanent magnet was proposed, which could effectively reduce the influence of permanent magnet segmentation on the back electromotive force and output average torque of motor. In addition, based on the improved nonuniform permanent magnet segmentation, a new method of unequal thickness and nonuniform permanent magnet segmentation was proposed. Three methods of uniform permanent magnet segmentation, nonuniform permanent magnet segmentation and unequal thickness and nonuniform permanent magnet segmentation were verified and compared by the finite element method. The simulation results showed that the cogging torque attenuation effect of the new method of unequal thickness and nonuniform permanent magnet segmentation was the best.