Abstract: In order to make it work well under complex electromagnetic environments, the electronic system is usually required to be installed in the shutter. However, for the ventilation and heat dissipation, it is inevitable to make some tiny apertures on the shielding wall. In order to solve the computational problem of terminal responses of the transmission lines in the double-layer shielding cavity with apertures excited by the exterior field, this paper presents a hybrid method. First, the response voltages are computed in the exterior layer shielding cavity by the transmission line model. After the response voltages transmitted into the equivalent magnetic currents, the BLT equation based on the electromagnetic topology theory can be used to compute the induced voltage of the transmission line in the double-layer shielding cavity. Finally, the numerical results show that the terminal response of the transmission line in the double-layer cavity is weaker than that in the single-layer cavity. And the response of the transmission line reaches its maximum value near the cavity and slot resonance. The analytic results give reference to electromagnetic compatibility and the design of the protection of electronic equipment against the external source.