Dimethyl Methylphosphonate(DMMP) and Ethylene Glycol(EG) as raw meterials, p-toluenesulfonic acid(p-TSA) and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) as synergetic catalysts, a novel polyphosphonate flame retardant was synthesized in a distillation apparatus. The molar ratio of raw meterials, the amount and molar ratio of catalysts and reaction temperature were investigated by L9(33) orthogonal experiment. The optimal synthesis conditions were as follows: the molar ratio of EG to DMMP is 1:1, n([Bmim]BF4)/n(DMMP)=0.01, n(p-TSA)/n(DMMP)=0.02, the reaction temperature at 155-170℃, reaction time at 4h. The synthetic product was yellowish transparent liquid and its acid value was 370 mgKOH/g. The product was characterized by IR and LC-MS analysis and the result showed that the product is a mixer of different polymers. The composition by side reactions which are mainly methanol, dimethyl ether, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether and ethylene glycol reduction were characterized by IR and GC-MS analysis.