The electromagnetic noise of permanent magnet synchronous motor (PMSM) for vehicles is the main source of new energy vehicle noise, which directly affects the vibration and noise characteristics of the vehicle. The low-order radial electromagnetic force acting on the stator structure of the motor is the main reason for the electromagnetic noise of the motor. Taking a PMSM for new energy vehicle with a rated power of 35 kW as the research object, an optimization method with auxiliary slots on the outer edge of the rotor is proposed to reduce the vibration and noise of the motor. The optimal parameter values are determined by multivariate optimization of multiple parameters of the auxiliary slot. The finite element method is used to compare the vibration and noise of the motor with and without the auxiliary slots. Finally, the correctness of the method is verified by the vibration and noise experiment of the prototype. Through the optimization of the rotor with auxiliary slots, the amplitude of the motor vibration acceleration is reduced by 2g and the noise is reduced by 4 dB.