Abstract: Multi-walled carbon nanotubes (MWCNTs) have attracted much attention in the field of gas separation membranes due to their unique one-dimensional structure and high specific surface area. However, their poor compatibility with polymer matrices and easy agglomeration limit their application in mixed matrix membranes (MMMs). In this study, surface-functionalized Si-MWCNTs were prepared by combining acidification treatment with silane coupling agent (APTES) modification, and Si-MWCNTs/PI mixed matrix membranes were prepared by blending Si-MWCNTs with fluorinated polyimide. The structure and properties of the filler and membrane materials were systematically studied by means of FT-IR, TGA, XRD and gas permeability. The results show that the introduction of —OH and —NH₂ functional groups on the surface of Si-MWCNTs effectively enhances its interfacial compatibility with polyimide and avoids disordered agglomeration. Its tubular structure provides a fast diffusion channel for gas molecules and improves the permeability of the membrane material. When the loading amount of Si-MWCNTs was 2wt.%, the CO₂ permeability coefficient increased to 35.63 Barrer, which was 69% higher than that of the pure membrane, and the CO₂/N₂ separation factor reached 24.83, an increase of about 85%; in particular, the O₂/N₂ separation performance exceeds the 1991 Robeson upper limit. The results show that Si-MWCNTs effectively break through the trade-off between permeability and selectivity of traditional polymer membranes in gas separation by synergistic structural regulation and interface optimization, showing good application potential.