Abstract: In recent years, the construction of large radio telescopes in China has been accelerated, and the project of ultra-high electromagnetic shielding technology should be extremely urgent. In this paper, the relationship between the shielding effectiveness of multi-layer shielding shell in non-interconnected state and the number of layers is theoretically deduced and analyzed. According to the measurement method of GB/ T 12190 electromagnetic shielding chamber shielding effectiveness, the single-layer, double-layer and three-layer predictive analysis models are established, and the shielding effectiveness of different levels of shielding is predicted and analyzed by using the dominant main path method, and the relationship between the multi-layer shielding level and the shielding effectiveness of the non-interconnected state is verified by comparing with the theoretical calculation results, which providing technical and theoretical support for the construction of ultra-high shielding environment for large radio telescopes.