Abstract: A novel flame retardant containing phosphorus and nitrogen (PNFR) was synthesized by the reaction between 1, 3, 5-tris(2-hydroxyethyl)isocyanurate(THEIC) and phenyl dichlorophosphate(PDCP), and its structure and composition were characterized by FTIR, nuclear magnetic resonance spectroscopy (¹H-NMR and ³¹P-NMR), respectively. PNFR was compounded with ammonium polyphosphate(APP) applied to prepare ammonium polyphosphate-novel flame retardant and polyurethane foam (APP-PNFR/PUF) composites, and the flame retardancy and thermal property of APP-PNFR/PUF composites were respectively investigated by limiting oxygen index (LOI), vertical burning testing, cone calorimeter testing and thermogravimetric analysis. The results show that the PNFR is successfully prepared. TGA of PNFR suggests that it has good thermal stability with initial degradation temperature 249℃, and the residue of PNFR is 33.7% at 800℃ under nitrogen atmosphere. The addition of APP-PNFR effectively enhances the flame retardany of polyurethane foam(PUF), and especially when the loading amount of PNFR is 7.5% based on the premixed polyether polyols' weight, the APP-PNFR/PUF has optimum comprehensive properties with LOI increasing from 19% to 24%, and UL-94 vertical burning grade reaching V-0 level. Meanwhile, the peak heat release rate of APP-PNFR/PUF3 decreases from 110.6 kW/m² to 94.5 kW/m². Additionally, the initial degradation temperature of APP-PNFR/PUF3 increases by 6℃, maximum decomposition rate decreases by 16.3%, and the residue is 33.5% at 800℃ under nitrogen atmosphere. The incorporation of PNFR does not impair the physical mechanical property of PUF.