Abstract: Accurate calculation of transformer winding temperature rise and hot spot need to consider the influence of winding interturn insulation, but the workload of fine modeling and the amount of meshing considering winding interturn insulation are very large. To solve this problem, this paper presented a method based on the minimum thermal resistance rule to calculate the equivalent thermal conductivity of oil-immersed power transformer windings. The axial equivalent thermal conductivity and radial equivalent thermal conductivity of oil-immersed power transformer windings were calculated respectively. In this way, the cake winding with equivalent thermal conductivity can be obtained to simulate the actual winding structure considering the interturn insulation. In order to verify the effectiveness of the proposed method, a simulation model of the temperature rise of the oil-immersed transformer windings was established, and the simulation results on temperature rise and hot spot of equivalent model were compared with the simulation results of actual model considering interturn insulation. The results show that the temperature rise and hot spot location are basically the same, and the equivalent model reduces the mesh profile component by 72%, which verifies the effectiveness of the proposed method. The proposed method is applied to the temperature rise and hot spot analysis of the grid side and valve side windings of the converter transformer, and the winding temperature rise and hot spot distribution of the converter transformer are obtained.