The invention relates to the field of chemical technique, especially to a production method for preparing monopotassium phosphate and a by-product a special fertilizer for strawberry. By changing coefficients such as temperature and the like of wet-process phosphoric acid preparation of monopotassium phosphate, purity of the product monopotassium phosphate is raised, and a compound fertilizer containing N, P and K combined forms can simultaneously be produced. In addition, a filtrate is adjusted to acid, and a formaldehyde solution is added to prepare a controlled-release compound fertilizer. By the method, purity of monopotassium phosphate can be raised, and the produced special fertilizer for strawberry has good absorptivity. Meanwhile, the produced special fertilizer for strawberry can meet nutritional requirements of each period of growth cycle of strawberry. By the use of the compound fertilizer, yield of strawberry is raised greatly. The special fertilizer is an efficient compound fertilizer.