Bromomethylimidazole modified melamine oligomer catalyst(CN MIm) was prepared by two-step method. The structure, morphology and thermal stability of catalyst were characterized by FTIR, XRD, SEM, TG and XPS. The results showed that the imidazole based ionic liquid was successfully loaded on the oligomer of melamine and had good thermal stability. The effects of reaction conditions on the cycloaddition performance of epichlorohydrin(ECH)and CO2 were investigated. Using CN MIm as catalyst, under the conditions of reaction temperature of 120 ℃, reaction time of 1.5 h, CO2 pressure of 2.0 MPa and mass ratio of catalyst to ECH of 0.036, the conversion of ECH and the yield of chloropropylene carbonate(CPC) were 99% and 98%, respectively. Meanwhile, CN MIm had good universality for different epoxides. In addition, the synergistic catalytic reaction mechanism of cycloaddition of epoxide and CO2 by bromine ion in hydroxyl, amino and imidazole based ionic liquids contained in melamine oligomers was proposed.