NOVELTY - Preparing potassium dihydrogen phosphate byproduct and towel gourd fertilizer comprises e.g. mixing phosphoric acid and carbamide, raising temperature, reacting under stirring condition to obtain an intermediate material slurry, mixing the intermediate material slurry and alkaline potassium salt, completing reaction to obtain material slurry containing nitrogen, phosphorus and potassium, performing cooling crystallization process, filtering, analyzing and detecting the filtered liquid, stopping crystallization and filtration process to obtain filter cake, and adding trace element compound.    USE - The method is useful for preparing potassium dihydrogen phosphate byproduct and towel gourd fertilizer (claimed).    ADVANTAGE - The method provides the composite fertilizer, which maximizes the requirements of crops; avoids mismatches of elements, which reduces composite fertilizer production and resulting in high cost; and avoids addition of excessive elements in the soil, which results in soil solidification and environmental pollution.    DETAILED DESCRIPTION - Preparing potassium dihydrogen phosphate byproduct and towel gourd fertilizer comprises mixing phosphoric acid and carbamide according to mol ratio of (1.1-1.3):1, raising temperature to 90-100 degrees C at a heating speed of 10 degrees C/minute, reacting under stirring condition for 4-5 hours to obtain an intermediate material slurry, then mixing the intermediate material slurry and 1.4-1.5 mol alkaline potassium salt, completing reaction to obtain material slurry containing nitrogen, phosphorus and potassium, placing the material slurry in a cooling crystallizer for performing cooling crystallization process, filtering, then placing the filtered liquid in the cooling crystallizer for circulating crystallization process, analyzing and detecting the filtered liquid, when the content of nitrogen is 15-16%, phosphorus pentoxide content is 7-8%, and potassium oxide content is 8-9%, stopping crystallization and filtration process to obtain a filter cake, i.e., potassium dihydrogen phosphate product, then adding trace element compound to the filtrate to adjust the chemical form of fertilizer to obtain a fertilizer primary product, then placing the fertilizer primary product in a drier, raising temperature to 45-55 degrees C under heating speed is 3 degrees C/minute, drying for 0.5-1 hour, and adjusting water content to 3-4% to obtain towel gourd fertilizer.