Abstract: In order to reduce the magnetic leakage of the permanent magnet synchronous motor and reduce the torque pulsation and cogging torque, a method of adding a double-layer U-shaped magnetic barrier inside the rotor is proposed. The expressions of the air gap flux density, torque pulsation and cogging torque are derived after increasing the magnetic barrier in combined pole permanent magnet synchronous motor, so as to analyze the mechanism of the structural parameters of the magnetic barrier affecting the amplitude of the air gap flux density and weakening the torque pulsation and cogging torque. To explore the optimal position and the opening angle of the magnetic barrier, the air gap flux density, torque pulsation and cogging torque are used as optimization objectives and the adaptive genetic algorithm is used for multi-objective optimization. The results show that adding magnetic barrier in rotor can effectively raise the air gap flux density amplitude, reduce the torque pulsation and cogging torque. The value of torque pulsation of the optimized motor is reduced by 7.62%, The value of cogging torque is reduced by 22.67%, and the amplitude of the air gap flux density is improved by 3.33%. The proposed method improves the motor's output performance by adding magnetic barrier in rotor, which provides reference for the optimization analysis of electromagnetic characteristics of the same type of motor.