This invention discloses a method for producing storage-increasing compatilizer for soil from domestic oven slag. The storage-increasing compatilizer is composed of: domestic oven slag 35-45%, potassium dihydrogen phosphate 10-20%, diammonium phosphate 15-20%, rape residue 10-15%, urea 1-3%, and high-fat film 1-2%. The method comprises: (1) selecting domestic oven slag, pulverizing and milling to below 1 mm (20 mesh); (2) air-drying the auxiliary materials, pulverizing, milling, and sieving with 20 mesh sieve; (3) mixing, stirring uniformly, and packaging or granulating. The storage-increasing compatilizer is applied by 750-1500 kg per ha soil, and can increase cotton yield by more than 12%, and increase water utility by more than 10%. The storage-increasing compatilizer can also retain water and fertilizer, and improve soil fertility.