The invention relates to isophorone, in particular to a catalyst used for synthesizing isophorone and a preparation method thereof. The catalyst used for synthesizing isophorone is prepared from components including MgO and ZrO2, wherein the mole ratio of MgO to ZrO2 is (0.1-2):1. The preparation method includes the steps that 1, polyvinylpyrrolidone K30 is dissolved in absolute ethyl alcohol, then magnesium nitrate hexahydrate is added into the solution to prepare a solution A, and zirconium propoxide and acetylacetone are added into absolute ethyl alcohol to prepare a solution B; 2, the solution B is added into the solution A to be stirred, then deionized water is added to obtain a thick solution, and the thick solution stands to be converted into gel; 3, reflux and filtration are performed on the gel in ammonia water, a filter cake is dried and then calcined, and then the catalyst used for synthesizing isophorone is obtained. The catalyst has high activity and selectivity, the conversion rate of acetone can reach 54.6%, and the overall selectivity of isophorone and mesityl oxide can reach 96.8%. The catalyst is easy to prepare and good in stability.