Abstract: The law of chelated Zn by ammonium polyphosphate was studied，with watersoluble ammonium polyphosphate and zinc sulphate as raw materials.Ammonium polyphosphate and its chelated product were characterized and the preparation of chelated product was tested.The effect of temperature and pH on the capacity of chelated zinc by ammonium polyphosphate by FBRM was investigated.The results indicated that the chelating capacity of ammonium polyphosphate on Zn gradually reduced with the raising of temperature（5~40 ℃） when pH was kept constant.In addition，the chelating capacity showed a trend of de creasing first and the increasing with the increase of pH（5~8） and the chelating capacity reached 0.024 3 g/g（per 1 g APP） when pH=5.5.A dimensionless equation was developed to predict operational conditions of chelating capacity，temperature and pH.

Key words: ammonium polyphosphate, chelation, zinc