Abstract: An amino resinous intumescent flame retardant was synthesized. Its composition was a caged bicyclic macromolecule containing phosphorus characterized by Fourier transform infrared(FTIR), which was applied to flexible polyurethane foam (FPUF). 30% weight of flame retardants were added into FPUF to get 26.5％ of the limiting oxygen index. Cone calorimeter data showed that the release of heat, smoke and gas was much decreased while the activation energy for the decomposition of sample has been decreased by 54kJ·mol<sup<-1</sup<, which showed that the intumescent flame retardant (IFR) can catalyze decomposition and carbonization of the FPUF.