Abstract: The preparation of porous membrane by supercritical CO2 fluid is a new method with many advantages. In this paper，the principle of preparation is introduced，and the influences of such conditions as pressure，concentration of polymer，temperature are analyzed. The final structure of porous membrane is decided by the diffusion speed of supercritical CO2 fluid inside the polymer and the plasticizing effect of polymer caused by supercritical CO2 fluid. In addition，the unique advantage sof the method is summarized.