The analysis of the lightning overvoltages of the distribution network is related to safe and reliable power supply of the power system, which needs to be paid attention to. However, the structure of the distribution network is complex, and an effective analysis is difficult to achieve through the use of classic transmission line equations. Therefore, in this paper, the electromagnetic topology method, which is suitable for the synchronous solution of the electromagnetic response at the junctions of the complex system, is introduced into the analysis of the lightning overvoltages in the distribution network. First, the BLT equation suitable for transmission line networks is provided and the construction methods of its elements are shown; then, the analysis process of electromagnetic topology is demonstrated in detail with an example of a complex distribution network, and the solution steps of the scattering matrix of the ideal junction are shown emphatically. The results show that the electromagnetic topology method is applicable to the analysis of the lightning overvoltages at the junction of the distribution network, as the calculation results are quite consistent with the results of CST, and the time consumed is much less than CST.