The invention discloses a method for promoting the synthesis of a dihydropyrimidone compound by utilizing dihydrogen phosphate ionic liquid, which belongs to the technical field of the synthesis of dihydropyrimidone compounds. The method provided by the invention is characterized in that a N-propargylamide compound and p-toluenesulfonyl azide are taken as reation substrate, CuI is taken as catalyst and dihydrogen phosphate ionic liquid is taken as promoter and solvent are stirred under 70 DEG C to react, so that the target product, i.e., the dihydropyrimidone compound, is prepared. The preparation process of the dihydrogen phosphate ionic liquid provided by the invention is simple and convenient, the dihydrogen phosphate ionic liquid is cheap and easy to obtain, the catalytic activity is high, and the proceeding of the reaction can be effectively promoted; the reaction does not require the addition of alkali and ligand, and in air atmosphere, ideal reaction yield can be obtained withina short time; the reaction system does not corrode equipment, and does not have special requirement on a reaction vessel, and moreover, both the operation and post-treatment processes of the catalytic system are simple.