A novel silicon-containing hyperbranched polyphosphonate acrylate (HPA), successfully synthesized via the Michael addition polymerization of tri(acryloyloxyethyl) phosphate (TAEP) with (3-aminopropyl)trimethoxysilane (KH550), was incorporated into the epoxy acrylate resin (EA) to prepare UV-curing flame retardant coatings. The study of thermal degradation of these coatings revealed that HPA can catalyze the degradation of EA, contributing to the formation of thermally stable char layer. The residues of EA/HPA-3 (which contains 30 wt % HPA) at various temperatures were analyzed by X-ray photoelectron spectroscopy (XPS) and the results displayed that phosphorus and silicon elements can well protect the carbonaceous char from thermal-oxidative degradation at 600 degrees C, but do not work at 800 degrees C. Besides, the investigation of the flammability illustrated that the addition of HPA increased the limiting oxygen index (LOI) value and reduced the peak heat rate release (HRR) and total heat release (THR).