Abstract: Calcium biphosphate is an important product in fine processing wet-process phosphoric acid（WPA），it conforms to the present market needing to develop the middle production of calcium biphosphate refined series product，and is of great significance.Process conditions of preparation of sodium dihydrogen phosphate with double decomposition reaction between calcium biphosphate and sodium sulfate were studied，and product by concentrated crystallization process was obtained.Influences of the reaction temperature，mix ratio of sodium sulfate to calcium biphosphate，ratio of liquid to solid，and reaction time on P2O5 recovery were investigated.Optimal process parameters of the reaction obtained were as follows：the reaction temperature was 50 ℃，mix ratio of sodium sulfate to calcium biphosphate was 1.2∶1，mass ratio of liquid to solid was 4∶1，and reaction time was 120 min.Under the conditions，the P2O5  recovery was 79.1%.Advantages of this process were the purity of product was high，process flow was short，and operation was simple etc.

Key words: sodium dihydrogen phosphate；calcium biphosphate；crystallization；P2O5 , recovery