Abstract: A novel reactive flame retardant (DOPO-PHBA) was synthesized by the reaction between 9,10-dihydro-9-oxa-10-phosphine-10-oxide (DOPO) and p-hydroxybenzaldehyde (PHBA).Its structure and composition were characterized by FTIR and nuclear magnetic resonance spectroscopy ¹H-NMR and ³¹P-NMR. DOPO-PHBA was compounded with triglycidyl isocyanurate (TGIC) to prepare DOPO-PHBA-TGIC/epoxy resin(EP) composites. The flame retardancy and thermal properties of DOPO-PHBA-TGIC/EP composites were respectively investigated by limiting oxygen index (LOI), dynamic mechanical analysis (DMA) and thermogravimetric analysis. Results indicate that DOPO-PHBA is successfully synthesized. The addition of DOPO-PHBA-TGIC can significantly enhance the flame retardancy of EP resin, while the mass fraction of phosphorus is 0.6wt%, LOI value increases from 24% to 32.5%. Additionally, the glass transition temperature (T_g) of DOPO-PHBA-TGIC/EP composites with different phosphorus mass fractions are maintained at 200℃ or higher, and the residues at 800℃ under nitrogen atmosphere are increased. But the initial degradation temperatures and maximum decomposition rates of DOPO-PHBA-TGIC/EP composites are decreased. FTIR analysis of char residues reveal that this flame retardant system satisfies condensed phase flame retardant mechanism, and the incorporation of DOPO-PHBA-TGIC does not impair the physical property of EP resin.