Ammonium polyphosphate(APP) is an excellent, high-efficiency and nontoxic inorganic flame retardant, used as the necessary flame-proof additive for all kinds of expanding-type flameproof paint and flame retardant products. The polymerization degree of our ammonium polyphosphate(APP-I) is higher than 50; the solubility in water is lower than 2g in every 100ml water.