Different from conventional natural cooling or housing water cooling motor, water is directly used by the internal submersible motor to cool the inside of the motor, which leads to the strong coupling of fluid-solid conjugate heat transfer of the whole machine. In order to improve the reliability and safety of the motor, the coupled heat transfer analysis of flow and temperature fields is very necessary. For a marine air-gap water cooling internal submersible permanent magnet motor, based on the principle of computational fluid dynamics (CFD), the three-dimensional flow and temperature fields are numerically simulated and the geometric structure is improved, eleminating the countercurrent phenomenon of the internal flow field of the motor, improving the heat dissipation efficiency of the whole machine, and optimizing the flow field and temperature rise of the motor. The result has a certain reference significance for the geometric structure design of the internal submersible motor.