An ultraviolet (UV) curing phosphorous-nitrogen contained flame retardant resin (TIDG) was first synthesized by reaction of tris (2-hydroxyethyl) isocyanurate (THEIC), itaconic anhydride (ITA), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and glycidyl methacrylate (GMA). The obtained TIDG was then mixed with polyurethane acrylate (PUA) resins and cured by UV light irradiation. Mechanical properties, thermal stability, combustion properties, and flame retardant mechanism were investigated using universal testing machine, thermogravimetric analyzer, cone calorimeter scanning electron microscope and Raman spectra, respectively. The results showed that the adhesion strength, tensile strength and pencil hardness of the PUA/DITG coating were all improved compared to pure PUA coating. The amount of carbon residue of PUA/DITG coating increased with the content increase of TIDG. In addition, compared with the pure PUA coating, the peak heat release rate and the total heat release of the PUA/40 wt% TIDG coating were reduced by 35.2% and 42.1%, respectively. Furthermore, the phosphorus-nitrogen synergistic flame retardant effect of PUA/DITG coating was demonstrated by scanning electron microscopy and Raman tests to accelerate the formation of dense and expand carbon layer.