Abstract: The copolymers of methacryloyloxy-［ethoxy］ trimethylsilane and acrylonitrile were prepared by bulk polymerization using azobisisobutyronitrile as initiator. The average molecular weight of the copoly-mer was measured by gel permeation chromatograph. The structure of copolymer was analyzed by infrared spectrometer and X-ray diffractometer. DSC was used to study the thermal property of copolymer membranes. The gas permeation property of copolymer membrane was characterized by gas permeability apparatus. Results showed that average molecular weight of the copolymer increased with the content of methacryloyloxy-［ethoxy］ trimethylsilane increasing. There were both amorphous and crystalline in the structure of the copolymer, with glass transition temperature about 51 ℃. The copolymer membrane showed CO2 permeability preferentially. At 23 ℃，0.1 MPa, the CO2 permeability coefficient and CO2/N2 selectivity factor were 129 Barrers and 11.8, respectively.