Abstract: Supersaturation is generally quite large in the process of reactive crystallization，a large number of tiny particles will emerge.Agglomeration will be formed because of the interaction between these tiny particles，affecting parameters，such as crystal size distribution，purity，crystal morphology, and tap density，of final product.Agglomeration can be easily found in the preparation of feed-grade calcium hydrogen phosphate.The pH range of agglomeration formed and the forming reasons were explored and analyzed.Some neutralization conditions affecting calcium hydrogen phosphate agglomeration were studied.Results showed that agglomeration formed at pH of 2.82~3.60，and raising temperature and stirring speed will reduce agglo- meration.Finally，an agglomeration-size model was established.

Key words: feed-grade calcium hydrogen phosphate, agglomeration, crystallization, agglomeration-size model