The paper proposes a method of thermal calculation of submersible electric motors intended for use at the stage of their conceptual design. The model is based on the complete system of hydrodynamic equations averaged over the motor cross section and the annular channel through which coolant is pumped. All geometric dimensions and properties of the substance are set. The temperature distribution over the cross section and along the length of the motor is calculated. Two approximations are used. In the first one, the temperature distribution in the cross section of the electric motor was averaged over the corners, which requires setting an effective coefficient of thermal conductivity inside the stator grooves filled with winding wires and electrical insulation. In the second approximation, the heat transfer at the solid – liquid interface was specified through the empirical dependence of the Nusselt number on the Reynolds and Prandtl numbers. To verify the model, the results obtained were compared with calculations by the method of computational fluid dynamics in the ANSYS Fluent software package. The error in calculating the insulation temperature was not more than 5%.