Aiming at the problem that the motor for vacuum dry pump drive is seriously heated when working in extreme vacuum environment, a 4.5 kW flux switching permanent magnet synchronous motor (FSPMSM) is taken as the research object to analyze its cooling structure, and the temperature field simulation calculation is carried out. The three-dimensional temperature field simulation calculation model of the FSPMSM is established by finite element software. The boundary conditions and heat source excitation are set to obtain the temperature distribution of each component inside the motor. The influence of the diameter of the water channel section and the number of water channel turns on the temperature change of the motor is analyzed. The temperature field comparison analysis with a permanent magnet synchronous motor (PMSM) with the same technical requirements under the same cooling conditions shows that the motor design is reasonable. Compared with the traditional PMSM commonly used in vacuum dry pump, this motor can better reduce the loss and reduce the temperature rise, which provides a certain reference for the development of new products of FSPMSM for vacuum dry pump.