Abstract: An Epoxy/Brominated Epoxy/Cyanate Ester co-curing system was studied for liquid oxygen compatible matrix resins, and a kind of imidazole 2E4MZ was introduced to the co-curing system. The gel times of the co-curing system at different temperatures indicate that 2E4MZ could effectively accelarate the co-curing reactions no matter whether epoxy or cyanate ester was excessive, which were confirmed by the FT-IR results. The FT-IR results also show that the cured resin structures are improved by 2E4MZ with more co-curing structures such as oxazoline and oxazolidinone. The thermal analysis, flash point and oxygen index results indicate that the cured resin modified by 2E4MZ have better anti-oxidation and flame retardant properties. The liquid oxygen impact test results approve that the cured resin modified by 2E4MZ have better compatibility with liquid oxygen. This kind of modification is an easy and cheap way for epoxy systems to get better compatibility with liquid oxygen.