Abstract With the development of China’s urbanization construction, the proportion of urban power distribution cables is increasing. The existing models for the temperature calculation of urban medium and low voltage three-core cables regard the filler layer and inner sheath as isothermal body structure for research and analysis, and do not take into account the temperature inhomogeneity characteristics of the three-core cable structure itself. In the paper, the uneven distribution characteristics of the buffer layer of the three-core cable are considered, and then the temperature distribution of the inner sheath is analyzed, and the distributed modeling of the inner sheath is carried out by drawing on the idea of analogous distributed model of the electric circuit, and from the heat flow theory, the heat flux assigned to each segment of the structure such as each inner sheath is derived, and the steady-state thermal circuit model of the three-core cable is established based on the principle of equivalency, and the finite element computation method is adopted to recognize the thermal circuit parameters, and finally, after the simulation results are compared with the simulation results, the temperature of the three-core cable structure itself is considered as an isothermal structure. Finally, after comparing with the simulation results, the accuracy of the thermal circuit model reaches 95%, the change of ambient temperature has less influence on the thermal circuit model, and the model has high robustness, which provides support for the on-line detection technology of the state of three-core cables.