Abstract: abstract: In view of the flammability problem of rigid polyurethane foam used in building insulation materials, the rigid polyurethane foam is chemically grafted and modified to make the melamine groups uniformly dispersed in the flame-retardant material system. Through flame-retardant performance test, mechanical performance test, combustion performance test and scanning electron microscopy analysis, the flame-retardant performance, compression performance and smoke suppression performance of the material in the magnesium hydroxide/ammonium polyphosphate system are investigated. The experimental results show that the melamine structure modification can greatly improve the flame retardant performance of pure polyurethane materials under the condition that the compression performance of the material is less weakened, and the limiting oxygen index can reach 26.4% without adding any flame retardant. In the flame-retardant system with ammonium polyphosphate, the limiting oxygen index can reach 28.4%, while meeting the UL-94 V0 level. The minimum heat release rate of the modified composite material can reach 101.9 kW/m2, which could be reduced by 35.3% as much as that of pure polyurethane material, and the smoke emission rate generated during combustion can be reduced by 56.6% as compared with pure polyurethane material，and the carbon is dense and has a good flame retardant effect.

Key words: Key words: rigid polyurethane foam, melamine modification, magnesium hydroxide, ammonium polyphosphate