The thermal field distribution of generator has a great influence on the failure phenomenon of the overheat protection component, which is the key parameter to be considered in the design. Based on the steady-state pressure solver and turbulence model in ANSYS software, the internal thermal field distribution of the motor under fault mode was simulated. The thermal field distribution of the stator, rotor and shell circulating oil circuit were obtained. The results show that the simulated thermal field is consistent with the actual temperature field distribution. The temperature gradient of low-melting alloy in the thermal trip mechanism is accordance with the internal thermal field distribution of the generator. It is helpful to protect the motor from overheating by changing the melting points of some key parts and the special softening temperature points of materials.