Nowadays, electromagnetic wave radiation is one of the sources of environmental pollution, which seriously affects human health and and the environment. Fiber paper made from high-performance fibers has shown potential for use in the electromagnetic interference (EMI) shielding due to adapting different complex working environments. However, achieving lightweight, high-efficiency, and flexible electromagnetic shielding remains challenging. To address this issue, we design a lightweight polysulfonamide/polyurethane-CNTs@Ag (PSA/PU-CNTs@Ag) fiber paper with double-layered structure and high electromagnetic shielding efficiency (EMI SE) via vacuum-assisted filtration and heat treatment. The results show the content of Ag nanoparticles 0.3 g in PSA/PU-CNTs@Ag fiber paper, the resistance is less than 1 Ω, the electrical conductivity reaches 883.57 S/m. At the same time, the thickness of Ag film increases, the EMI SE value reaches 90.537 dB. The EMI SE value of PSA/PU-CNTs@Ag fiber paper after folding one thousand times has decreased, but still maintains 95% of the original shielding performance. Moreover, its EMI SE values still maintain above 60 dB in various extreme environments (hot 150 °C, cold −70 °C). In summary, this work shows PSA based EMI shielding materials own excellent overall performance and hold broad different working extreme environments.