When the rear drive assembly of a self-developed new energy vehicle is unloaded, the NVH problem is caused by the tooth groove torque of the external rotor permanent magnet synchronous motor. In order to solve this problem, this paper takes the external rotor permanent magnet synchronous motor with the tangential magnetic circuit structure carried by the self-developed new energy SUV as the analysis object, and builds the mathematical model of tooth groove torque of the internal permanent magnet motor with the tangential magnetic circuit structure. Through simulation analysis, the influence degree of parameters such as the number of auxiliary slots on the stator tooth crown, slot depth, slot width and spacing on the tooth slot torque is obtained. Through simulation, it can be seen that each parameter has an influence on the tooth slot torque through mutual coupling. Finally, the optimization range of key influencing parameters is determined for multi-objective optimization, and the electromagnetic scheme with the minimum tooth slot torque is optimized for test verification. Successfully solved the NVH problem caused by the no-load condition of the powertrain.