Abstract: Conductive polymer composites (CPC) are gradually replacing traditional metal-based electromagnetic shielding materials due to their advantages of low price, light weight, high specific strength, corrosion resistance, and excellent shielding performance, etc. However, the traditional polymers are less resistant to harsh environments, such as extreme temperatures, acidic and alkaline solutions, which affects the electromagnetic shielding performance of CPC in harsh environments (EMI SE) and makes it difficult to satisfy the needs of special environments and other It is difficult to meet the needs of special environments and other fields. Therefore, it is still a challenge to explore flexible multifunctional EM shielding materials with simple preparation methods and suitable for extreme environments. In this paper, MXene-carbon black/polyimide (MXene-CB/MCP) composite films with high electromagnetic shielding efficiency were successfully prepared by the scraping method and thermal imidization process. Due to the good electrical conductivity of MXene and carbon black (CB) and the synergistic effect between them, the EMI SE and the ratio of electromagnetic shielding effectiveness to thickness (EMI SE/t) of the MXene-CB/MCP -35 composite film with a thickness of 80 μm were 24.06 dB and 300.75 dB/mm, respectively, in the frequency range of 8.2-12.4 GHz, and after complex environmental treatment, the composite film was successfully fabricated. The composite films show stable EMI shielding performance even after complex environmental treatment. In addition, the composite films have excellent mechanical properties, with the average tensile strength of the MXene-CB/MCP -35 composite film still reaching 100.40 MPa. The films also have excellent thermal stability and flame retardancy.