Abstract: The Coating the inner wall of the shielding cavity with absorbing materials can significantly improve the shielding efficiency of the metal cavity, but numerical calculation methods have lower efficiency in calculating the shielding effectiveness of the cavity. Therefore, this paper proposes an analytical method based on the BLT equation to calculate the shielding effectiveness of a rectangular aperture cavity with graphene, silicon carbide, polytetrafluoroethylene (PTFE), and Ni/rGO composite materials coated on its inner wall. By comparing the numerical simulation results of CST, the resonant frequencies of the cavity can be accurately calculated, with an average error of no more than 8 dB. This method has higher computational efficiency and requires fewer computational resources, the rapidity and effectiveness of the BLT equation analytical model are verified. At the same time, the influence of different thicknesses of graphene, silicon carbide, PTFE, and Ni/rGO composite materials coated on the shielding effectiveness of the cavity inner wall is analyzed. The results show that among the four materials, the higher the relative dielectric constant of the material, the greater the shielding effectiveness of the cavity; when PTFE material is coated on the inner wall of the cavity, the change in material thickness will not affect the resonant frequency of the cavity, and when 1 mm PTFE material is coated, the best shielding effect can be achieved; when coating the remaining three materials, the change in material thickness does not affect the resonance frequency at TE₁₀₁ and TE₁₀₂, but only affects the frequency of high order resonance TE₁₀₃. Moreover, when all three materials are coated with a thickness of 2 mm, the cavity shielding ability is the best.