Abstract: Polyvinylpyrrolidone was synthesized by radical polymerization.Poly(N-vinyl-γ-sodium aminobutyrate) containing secondary amine and carboxyl groups which can react reversibly with CO₂ was obtained through the hydrolysis of polyvinylpyrrolidone. A new facilitated transport composite membrane for CO₂ separation was prepared with the hydrolysate as the top layer material and microporous membrane as the support. The interactions of CO₂, CH₄, water, low-molecular-mass impurities in the membrane and support membranes were studied and the influences of the interactions on the membrane structure and performance were also investigated. Water was not only a carrier but also a plasticizer.The coupling between CO₂ and CH₄ affected their permeability.The presence of low-molecular-mass impurities in the membrane could alter the membrane structure and performance.The material and pore diameter of the support membrane affected the composite membrane performance.