The grafting polymerization of ionic liquids on silica surface was performed by the solution polymerization and surface-initiated atom transfer radical polymerization methods. The silica-immobilized ionic liquid polymers were characterized via FTIR, TG and SEM analysis. The CO2 adsorption property and the selectivity of CO2/N2 were investigated. The CO2 thermodynamic study and diffusion performance of silica-immobilized ionic liquid polymers was also discussed. The results show that loading amount of ionic liquid made by the surface initiated ATRP method is much higher than that of by the solution polymerization method. The sample prepared by solution polymerization method presents more developed porous structure, and the CO2 adsorption of them can reach 4.54 wt% at 273 K and 0.1 Mpa. The CO2/N2 selectivity of the silica-immobilized ionic liquid polymers is much better than that of the bare silica. The silica-immobilized ionic liquid polymers exhibit good CO2 sorption/desorption cycle capacity. The sorption of CO2 on silica-immobilized ionic liquid polymers is likely due to physisorption.The diffusion coefficients of CO2 adsorption on silica-immobilized ionic liquid polymers are much higher than that of the ionic liquid polymers.