Taking a rated power of 60 kW PMSM as the research object, the air gap equivalent thermal conductivity coefficient was used to deal with the heat exchange between the stator and rotor. The equivalent thermal model of the stator windings was given. Considering temperature effect on stator winding resistance in winding copper loss calculation, the thermal resistance between the housing and the stator core due to the assembly gap was test. On this basis, the finite element model of 3D global transient temperature field of PMSM was established, and the temperature field of motor at peak speed was calculated and verified by experiment. The optimization of channel width ratio, channel number and fin was carried out to find out the optimal solution. The results showed that the maximum temperature of the motor was decreased by 9.8 ℃ after the channel was optimized, which had a certain guiding significance for the structural design of the motor channel.