Poly(vinylamine)/poly(ethylene glycol) blend membranes were prepared. The effects of blend polymer composition on the membrane structure and CO2/CH2 separation performance were investigated. The results show that membrane crystallinity are at a minimum against poly(ethylene glycol)(PEG) content, while the permeation rates of CO, and CH, are the maximum. The blend membrane with 10wt% PEG has the highest pure CO, permeation rate of 5.8 x 10(-6) cm(-1) (STP)/cm(2).s.cm Hg and the highest selectivity of 63.1 at 25 degrees C and 96 cm Hg of feed pressure. The effects of cross-linking and the coupling effects between CO2 and CH4 were also investigated. The selectivity increased remarkably when the membrane is cross-linked. For mixed gas of constant CH, partial pressure and changing CO, partial pressure, the CH, permeation rate increased with an increase of CO2 partial pressure due to the coupling effects.