Abstract: Recent research progress in preparation and characterization of typeⅡ long-chain（polymerization degree≥1 000） ammonium polyphosphate（APP） was reviewed. A suitable calculation formula of APP polymerization degree for nuclear magnetic resonance method was given.It was pointed out that phosphoric-anhydride polymerization method replaced by non-anhydride polymerization method and crystal-type transition method，which have safe technical processes will be a development trend.The development and application of new type reactors，and the join uses of different characterization methods will become the focus of research.

Key words: typeⅡ long-chain APP, non-anhydride polymerization method, crystal-type transition method