Abstract: An electromagnetic topology (EMT) model is presented to solve the problem of electromagnetic pulse (EMP) coupling through an aperture to multi-conductor transmission lines inside cavity. The topological diagram and the interaction sequence diagram of the proposed model are constructed by using EMT theory. The aperture is replaced by the equivalent electric and magnetic dipoles sources which can be exciting sources inside cavity, the equivalent distribution sources on multi-conductor transmission lines are computed by the supermatrix integral transform. The simulation results of incident voltage and electric field shielding effectiveness (FSE) indicate the validity of the proposed model.