The invention discloses a method for preparing milrinone. The method comprises the following steps: (1) mixing 4-methyl pyridine and maleic anhydride in a solvent, adding a catalyst, maintaining the temperature to be 30-45 DEG C, continuously stirring, slowly adding propyl alcohol, reacting for 30-60 minutes, and finally evaporating and extracting so as to obtain 1-(4-pyridyl)-acetone; (2) adding triethyl orthoformate, maleic anhydride and maleic acid into a product prepared in the step (1), maintaining the temperature to be 20-45 DEG C, reacting for 1-3 hours, and evaporating so as to obtain 1-ethyoxyl-2-(4-pyridyl) vinyl methyl ketone; and (3) adding ethanol, acetone and propane dinitrile into the product prepared in the step (2), maintaining the temperature to be 40-65 DEG C, reacting for 1-5 hours so as to obtain crude milrinone, and purifying, thereby obtaining the pure milrinone. According to the method for preparing milrinone provided by the invention, reaction conditions are mild, the yield is high, the cost is low, the operation is easy and convenient and industrialized popularization and application are convenient.