In present work, crown ether-containing co-polyimide with improved gas permselectivity was developed for CO2/N-2 and CO2/CH4 separation. Crown ether segment grants the co-polyimide material good affinity with CO2 as well as strong rigidity of polymer chain. This co-polyimide was prepared by the condensation polymerization and chemical imidization of 4, 4-hexafluoro-isopropylidene diphthalic anhydride, 4, 4'-diaminodiphenylmethane and trans-di(aminobenze)-18-C-6 (trans-DAB18C6). The synthesized materials were characterized by FT-IR, H-1 NMR, XRD, TGA, DSC, GPC and electronic tensile machine. The fractional free volume (FFV) and fractional accessible volume (FAV) were calculated with molecular dynamics simulations. The mixed-gas permeation properties of the co-polyimide membranes were investigated to inspect the influence of trans-DAB18C6 content and feed gas pressure. Effects of testing temperature and humidity, casting solvent on membrane with 25 mol% trans-DAB18C6 were investigated. The molecular dynamics simulations results showed that (FAV)(CO2) decreased, while the ratios of (FAV)(CO2)/(FAV)(N2) and (FAV)(CO2)/(FAV)(CH4) increased progressively with trans-DAB18C6 content. The CO2 permeability increased firstly, and decreased subsequently with trans-DAB18C6 content. At the same time, both CO2/N-2 and CO2/CH4 selectivities increased progressively. The co-polyimide membrane with 25 mol% trans-DAB18C6 displayed the maximum CO2 permeability of 109.0 barrer and CO2/CH4 selectivity of 92.7, which surpassed the 2008 Robeson upper bound. The long term operation stability study demonstrated that the membrane had good stability.