Abstract: New polymeric membrane materials——polyvinyl amine (PVAm) with different primary amine contents were synthesized.By covering polyacrylonitrile(PAN) ultrafiltration membranes with PVAm, the PVAm/PAN composite membranes for CO₂/CH₄ separation were prepared. The composite membranes containing more primary amino groups have higher selectivity for CO₂/CH₄.The cross-linking of acid or glutaradehyde could improve the gas permselectivity of the composite membranes. With decreasing CO₂ content in the feed gas, the CO₂/CH₄ separation factor increased.When the feed gas was 25%(vol) CO₂ and 75%(vol) CH₄, the CO₂ permeation rate was 4.1×10^-9cm³(STP) •cm^-2•Pa^-1•s^-1, and the CO₂/CH₄ separation factor was 180.