Abstract: Based on the electromagnetic topology theory, the electromagnetic response of a complicated transmission line network is analyzed. Power network in a building is taken as an example and a topological model is established. The analyzed system is decomposed into nodes and tubes according to the electromagnetic topology theory, and a hybrid topological network considering the effects of radiation coupling and conductive coupling is constructed. The two coupling mechanisms can both be described by transmission matrix, scattering matrix and source matrix in the topological model. Using these matrices the BaumLiuTesche(BLT) equation is got and the terminal responses are calculated. Finally， the relationship between the voltage waveform and the terminal load is discussed.