In order to study the steady-state temperature field of a fully enclosed high-power permanent magnet traction motor under rated condition, a three-dimensional conjugate heat transfer model of temperature field of a permanent magnet synchronous traction motor with rated power of 815 kW is established based on the heat conduction model of the formed winding in slot. Considering the influences of rotating magnetization, stamping process and high-order harmonics of flux density on stator iron loss, and the influence of contact thermal impedance between water jacket and stator core on motor temperature rise, the Fluent software is used to solve the steady-state flow field and temperature field of the motor under rated condition. The average temperature rise of the winding and the local temperature rises at the measuring points at the stator core and the end of the winding are measured by the resistance method and the embedded temperature detector (ETD) method under the rated condition, and the absolute errors are -3.7 K, -0.3 K and 7.6 K, respectively. Furthermore, the flow field distribution characteristics of water and internal air path of the motor, the influence of the contact gap between water jacket and stator core on the average temperature rise of the winding, and the temperature rise distribution near the winding in the slot are analyzed. Finally, the design optimization direction of the motor cooling system is proposed.