Polymerized ionic liquids(PILs) are novel membrane materials with good CO2/N2 perm-selectivity. However, the industrial application of PILs is restricted by infrequent and expensive polymerizable ionic liquids. In this work, imidazolium-functionalized polysulfones (PSf-g-[MIm][Cl]) were synthesized by simple and controllable chloromethylation-Menshutkin two-step method. The effects of degree of Imidazolium (DIm), test temperature and pressure on the performance of the membrane were investigated. The results show that the membrane has a better pressure stability and the content of MIm is a critical factor on CO2 separation performance. As the content of MIm increases, CO2 permeability and CO2/N2 perm-selectivity improve obviously, attributing to the formation of continuous channel. Moreover, PSf-g-[MIm][Cl] shows excellent film forming ability even with a degree of imidazolium up to 172%, at 25 ℃, 0.4 MPa and humid conditions, the membrane shows good CO2 permeability of 66.4 barrer and CO2/N2 perm-selectivity of 118.4.