Production method for preparing ammonium polyphosphate from wet-process phosphoric acid serving as raw material

The invention discloses a production method for preparing ammonium polyphosphate from wet-process phosphoric acid serving as a raw material. The wet-process phosphoric acid serving as the raw material, a nitrogen-containing compound is added, the charge ratio of the wet-process phosphoric acid to a nitrogen source agent is (1.5-3):1, the wet-process phosphoric acid and the nitrogen-containing compound are put into a stirring type reactor, mixed uniformly and heated to 100 to 150 DEG C, and stirring reaction is conducted for 80 to 150 minutes under the conditions that the pressure is 0.1 to 0.3 MPa and constant temperature is maintained, so that an ammonium polyphosphate solution with low polymerization degree can be prepared. The wet-process phosphoric acid serves as the raw material, so that the production cost is obviously reduced, the polymerization degree n of the produced ammonium polyphosphate is less than or equal to 15, and the ammonium polyphosphate has full water solubility and can directly serve as