Abstract: Preparation technology data of ammonium polyphosphate（APP） were studied by using poly phosphoric acid and urea as raw materials.The whole process of APP′s poly condensation was composed of two steps: pre-polymerization and high-temperature ageing treatment.Effects of mix ratio of raw materials，reaction atmosphere，pre-polymerization temperature， ageing treatment temperature，and ageing treatment time etc.on the preparation process performance of product were discussed，respectively.The optimal process conditions of preparing low water solubility APP were obtained as follows：the amount-of-substance ratio of urea to poly phosphoric acid was 2.5∶1，the reaction went in the wet ammonia atmosphere，pre-polymerization temperature was 130 ℃，the polymerization temperature was 220 ℃，and the polymerization time was 150 min. Under those conditions，the water solubility of the prepared APP was 0.523 6 g per 100 mL H2O.The quality of the product met the Industrial APP Standard（HG/T 2770—2008） and the product′s crystalline form was a mixture ofⅠand Ⅱ proved by X-ray diffraction.

Key words: ammonium polyphosphate, poly phosphoric acid, urea, low water solubility