Electric vehicle traction motor is in the pursuit of high density, small and light weight, which constantly promotes the cooling and heat transfer technology and the development of the motor. So electromagneticthermal codesign method of traction motor was researched. By constructing an engineering stator thermal circuit model, the direct design method of stator winding thermal performance and key thermal parameters were proposed and directly applied to the electromagnetic design, which strengthened thermal performance design as well as made up for the defect of assessing the thermal performance by thermal load value in the traditional electromagnetic design. Thermal performance of different designs could also be compared through the rapid assessment of motor heat transfer ability and winding temperature rise, thus, get the best solution of electromagneticthermal codesign and enhance output torque during the motor continuous operation. A permanent magnet synchronous motor with liquidcoolinghousing was optimized by the direct design method of stator winding thermal performance, which could significantly reduce the stator winding temperature rise. At last, the temperature rise experiment verified the effectiveness of the direct design method of stator winding thermal performance as well as the evaluation of the thermal performance by the key thermal parameters.