The invention relates to the field of compound preparation, and discloses a preparation method of a beta-dione compound. The method comprises: in the presence of a solvent and alkali metal potassium alcoholate, reacting methyl carboxylate with ketone. The method is high in yield, is safe, and is suitable for industrial application. Particularly, when 3,5-heptadione is prepared through the method, the yield of 3,5-heptadione can reach more than 60%, wherein the yield is far more higher than that in the prior art by taking DMF as a solvent.