Abstract: The present invention discloses a preparation method for water-soluble potassium polymetaphosphate, and relates to the technical field of potassium polymetaphosphate production and preparation. In the present invention, potassium dihydrogen phosphate is mixed with a divalent cationic metal oxide at a mixing mass ratio of 70-90:5-18 to obtained a mixture, wherein the divalent cationic metal oxide is one or more of calcia, magnesia and zinc oxide in the field of food processing; then the mixture is heated and melted, and the temperature is kept constant for 1-3 h at a temperature of 600-700° C.; and after temperature keeping, the melted mixture is cooled naturally to obtain a product. The water-soluble potassium polymetaphosphate prepared by the present invention has a high water solubility and effectively solves the application defect of a traditional potassium polymetaphosphate product which is insoluble in water.