Abstract: A novel flame retardant containing phosphorous 2-methyl-3-(10-oxo-10H-9-oxa-10λ⁵-phospha-phenan-thren-10-yl)-propionic acid 2-hydroxy-ethyl ester(DOPOHM) was synthesized by 9-oxa-10-phospha-phenanthr ene 10-oxide(DOPO) and hydroxyethyl methacrylate (HEMA), and the flame retardant materials (ZnB-DOPOHM/AR) via were prepared via DOPOHM and various of ZnB adding into acrylate resin(AR). The thermal stability and flame retardant level of composites was characterized by TGA and LOI test. The synergies mechanism between DOPOHM and ZnB was studied by SEM, XPS and EDS. The degradation activation energies(E_a) of composites were calculated by Horowitz-Metzger theory. The results indicate that the thermal stability and LOI of composites is improved by ZnB content increasing. Moreover, the char layer after combustion become more compact and smooth due to effects of both two additives. The synergies mechanism reveal that progress of catalysis effect of decomposed phosphine on matrix occur on the surface of ZnO and B₂O₃ produced by ZnB, which is verified by ZnO-P₂O₅ existence. The calculated results show that ZnO and B₂O₃ positive catalytic role and synergic phosphine-catalyzed reinforce capability of char produced.