Abstract: A shielding effectiveness calculation model for cavity inner wall encapsulated graphene and composite absorbing material Ni/rGO was established based on the extended transmission line method (TLM) theory, considering the effective improvement of cavity shielding effectiveness by encapsulating absorbing materials on the inner wall of perforated metal cavity. Firstly, the equivalent circuit diagram of the calculation model is established according to the plane wave irradiation of the open cavity; then, the equivalent impedance analytical equation of the wave-absorbing material encapsulated in the inner wall of the cavity is derived; finally, the electric field shielding effectiveness of the established model is solved by applying the transmission line method. The results show that: in the set frequency range, the calculation results of this paper and the numerical simulation software CST calculation results match well, which verifies the validity of the extended TLM; compared with the empty cavity after encapsulation of wave-absorbing materials cavity shielding effectiveness will be significantly improved, and the larger the relative permittivity of the composite wave-absorbing materials on the electromagnetic shielding effect of the electromagnetic wave; encapsulation of wave-absorbing materials after the resonance frequency of the cavity will be offset; with the increase in the thickness of the encapsulated wave-absorbing materials cavity shielding effectiveness. The cavity shielding effectiveness increases with the increase of the thickness of the encapsulated wave-absorbing material.