Abstract: A containing phosphorus-boron hybrid polymer (PDCP-DGB) was synthesized by step-reaction polymerization using phenyl dichlorophosphate (PDCP) and boric diglyceride (DGB) as the raw materials. A series of PDCP-DGB/epoxy resin (EP) flame retardant composites were prepared by crosslinking and curing between PDCP-DGB and EP blends. The structure of PDCP-DGB was characterized by FTIR and nuclear magnetic resonance. The PDCP-DGB/EP composites were investigated by gel permeation chromatography (GPC), TG, limit oxygen index (LOI), microscale combustion calorimeter, SEM and XPS. The results indicate that with the increase of mass fraction of PDCP-DGB, the temperature of maximum decomposition rate of PDCP-DGB/EP composite, the residual mass rate and the LOI improve, but the smoke density level, maximum smoke density, peak value of heat release rate (PHRR) and total heat release (THR) decrease. PDCP-DGB is conducive to improve the thermal stability and flame retardant properties of PDCP-DGB/EP composite and has little influence on the mechanical properties of PDCP-DGB/EP composites. When the mass fraction of PDCP-DGB reaches 15wt%, the LOI reaches 28.3%, which is 47.4% higher than that of the pure EP, the vertical burning (UL-94) reaches V-0 level, the THR and PHRR decrease by 28% and 23%, respectively, the residual mass rate increases by 5.11%. SEM images show that the carbon residue surface of PDCP-DGB/EP composites is well improved, which is dense, continuous and smooth.