Due to the high power density characteristics of permanent magnet (PM) traction motors and the strict loading conditions of electric vehicle (EV) engine compartments, the excessive losses inside the motors can elevate rapidly the temperature rises, deteriorate the magnetic property of PMs, limit the output torques, and even cause the overheating damages of the machines. In order to guarantee the operational reliability, it’s of vital importance to research and develop the eff ective, reliable and economical cooling systems for improving the working performances of the PM traction motors. In this paper, the three-dimensional (3D) fl uidic-thermal coupled model of a high power density interior PM traction motor is established based on the basic theory of computational fl uid dynamics (CFD) and numerical heat transfer. The fl uid fl ow and thermal distributions are analyzed based on fi nite volume method (FVM), and verifi ed by experimental results. According to the heating characteristics of the motor, the external water frame structure of the motor shell is modifi ed to improve the cooling effi ciency. Taguchi method is used to optimize the cooling structural parameters, so as to reduce the steady-state temperature rise of the motor. The research work in this paper has certain reference signifi cance for the design and development of high power density PM traction motors used in EV applications.