The invention belongs to the field of chemical technology, and in particular to a synthetic method of gamma-alkyl oxyacyl methyl-gamma-butyrolactone and delta- alkyl oxyacyl methyl-delta-valerolactone. CuH compound as a reducing agent reacts with keto ester, alpha, beta-unsaturated carboxylic ester; keto ester, alpha,beta-unsaturated carboxylic ester, a silicon hydride or boron hydride react with each other with CuH compound as the catalyst; and other copper compound, phosphine ligand, silicon hydride or boron hydride react with each other to generate a catalyst, which directly catalyses silicon hydride or boron hydrogen to react with keto ester, alpha,beta-unsaturated carboxylic ester. The synthesis reaction is carried out through the above three methods. reaction of this three method of The method of the invention uses cascade reaction for synthesis, three steps of reaction are carried out continuously in the same reaction vessel; separation of intermediates is not required, so as to avoid the separation process and the resulting loss; and the method has simple operation, improved reaction efficiency, and good application value.