Load capacity and operating life are governed by the hot spot temperature of the transformer windings. A three-dimensional electromagnetic-temperature-fluid coupling model including the shell heat sink is established with an S20-M-630 kVA/10 kV oil-immersed distribution transformer as the research object. Aiming at the problems of complex internal structure of the winding, poor mesh quality of the fluid-solid boundary layer, and low computational efficiency, a winding parameter equivalence method and a hybrid mesh profiling technique combining mapping profilings and free profilings are proposed. The method not only significantly improves the accuracy of the calculation of the winding hot-spot temperature, but also optimises the mesh quality of the fluid-solid boundary layer, which significantly improves the calculation efficiency. The results show that in actual transformer operation, the winding temperature distribution can be effectively reflected by the winding parameter equivalence method, and compared with free profiling, hybrid profiling reduces the overall number of 3D meshes and simulation time by 73.60% and 82.50%. The relative error between the simulated and experimental values of the winding hot-spot temperature shall not exceed 1%.