NOVELTY - Diammonium phosphate is produced by concentrating wet diluted phosphoric acid dehydrate to obtain 30-40 wt.% phosphorus pentoxide (P2O5); settling and separating; sending the deposit to a wet diluted phosphoric acid dehydrate settling tank and sending the clear liquid for primary ammonization to obtain acidic ammonium phosphate slurry having degree of neutralization of 0.3-0.5; and carrying out second, third, and fourth ammonization until the degree of neutralization of acidic ammonium phosphate slurry is 1.6-1.9; and drying and sieving the slurry.    USE - Method for producing diammonium phosphate (claimed).    ADVANTAGE - The method can obtain diammonium phosphate with nitrogen-phosphorus ratio of 0.32-0.4, and reduce ammonia consumption and energy consumption. Further, the secondary ammonization and concentration integral device is energy-saving and environmental-friendly, and simplifies the technical equipment.    DETAILED DESCRIPTION - Production of diammonium phosphate comprises:    (A) concentrating wet diluted phosphoric acid dehydrate to obtain 30-40 wt.% P2O5;    (B) settling and separating the obtained material;    (C) sending the deposit at bottom part to a wet diluted phosphoric acid dehydrate settling tank and sending the clear liquid at upper part for primary ammonization to obtain acidic ammonium phosphate slurry having degree of neutralization of 0.3-0.5;    (D) carrying out secondary ammonization and acidic slurry concentration reaction to improve the degree of neutralization to 0.6-0.8;    (E) concentrating the slurry into final acidic ammonium phosphate slurry with water content of 15-20 mass%;    (F) carrying out third ammonization until the degree of neutralization of acidic ammonium phosphate slurry is 1.3-1.5;    (G) carrying out fourth ammonization until the degree of neutralization of the acidic ammonium phosphate slurry is 1.6-1.9; and    (H) drying and sieving the slurry to obtain the diammonium phosphate.    An INDEPENDENT CLAIM is included for a secondary ammonization and concentration integral device for producing diammonium phosphate, comprising a flash evaporation chamber, a dropping pipe, a lifting tube, and a reaction pipe which are sequentially connected one by one to form an annular sealed loop structure system. The top part of the flash evaporation chamber has a steam outlet. The dropping pipe has a discharge port. The reaction pipe is connected in series between the heater and the flash evaporation chamber, and has a gas ammonia nozzle. The lifting tube is connected in series with a forced circulation pump. The sidewall at the middle part of the flash evaporation chamber has a feed port.