The invention discloses a preparation method and application of a water-soluble water flush fertilizer for controlling soil-borne diseases and promoting crop growth. The fertilizer comprises, by weight, 17-21 parts of diammonium phosphate, 12-16 parts of potassium sulfate, 14-18 parts of straw, 13-17 parts of boric acid, 12-16 parts of magnesium sulfate, 9-13 parts of ferrous sulfate, 16-20 partsof animal waste, 18-22 parts of bentonite, 24-28 parts of urea, 19-23 parts of charcoal ash, 31-35 parts of seafood shells, 13-17 parts of indolebutyric acid, 7-11 parts of natural brassinolide, 16-20parts of expansin, 20-24 parts of chitosan oligosaccharide, 9-13 parts of lignin, 18-22 parts of bamboo vinegar, 19-23 parts of glucose and an appropriate amount of water. The fertilizer has high practicability, provides nutrients required for crop growth, has high fertilizer efficiency and can effectively control soil-borne diseases.