The invention discloses a formula for a coating-free slow-release synergistic sorghum blended fertilizer prepared from monoammonium phosphate blended with urea and potassium chloride. The slow-release synergistic sorghum blended fertilizer is prepared from 4.8-5.2 parts of urea, 1.8-2.2 parts of monoammonium phosphate, and 2.8-3.2 parts of potassium chloride, which are used as fertilizer sources, through stirring and mixing; three elements, namely nitrogen, phosphorus and potassium account for 51% of the slow-release synergistic sorghum blended fertilizer, wherein nitrogen accounts for 25%, phosphorus accounts for 8%, and potassium accounts for 18%. The fertilizer has an obvious slow-release synergistic characteristic; through the field test, and compared with the blended fertilizer prepared from other fertilizer sources, the blended fertilizer provided by the invention has the advantages that the yield is increased by 8%-10%.