Abstract: The polymerization conditions of ammonium polyphosphate (APP) were studied by microwave reactor and muffle furnace respectively with ammonium dihydrogen phosphate and urea as raw materials.During the synthetic process,the influences of different polymerization temperature,polymerization time,and mixing ratios of ammonium dihydrogen phosphate to urea on the content of P<SUB>2</SUB>O<SUB>5</SUB>,content of N,and the polymerization degree of APP were investigated.In the same requirement of product quality,the polymerization conditions in microwave reactor were more moderate and the microwave could also improve the polymerization of APP.The optimal process conditions were as follows:reaction temperature was&nbsp; 200 ℃,reaction time was 40 min,and amount-of-substance ratio of ammonium dihydrogen phosphate to urea was 1∶1.1.Under the above conditions,the mass fraction of P<SUB>2</SUB>O<SUB>5</SUB> and N were 69.05% and 14.13% in the products,and the polymerization degree reached 38.