As a new type of motor topology,modular stator permanent magnet synchronous motor is characterized by high fault tolerance and high torque density,but at the same time,there is the problem of large motor losses,which threatens the robustness of motor performance.A E-type modular stator permanent magnet synchronous motor was used as the research object,the motor loss mechanism was analyzed,and the motor loss change law under different operating conditions was studied.The thermal analysis of the motor was carried out by using the bi-directional magnetic-thermal coupling method,and the multi-objective optimization design of the motor was carried out by using the response surface optimization method based on the thermal analysis results.After optimization,the average output torque of the motor is increased by 14.15%,the eddy current loss is reduced by 55.99%,and the average temperature rise of the motor is reduced by 12.62%.Finally,the accuracy of the bi-directional magnetic-thermal coupling method and the effectiveness of the optimized design are verified by experiments.