The invention discloses a method for preparing 3,5,5-trimethyl-3-cyclohexene-1-one. The method comprises the following steps: taking 3,5,5-trimethyl-2-cyclohexene-1-one (alpha-IP) as a raw material, taking preazophosphorine as a catalyst, and carrying out an isomerization reaction by adopting a reactive distillation technique, thereby obtaining the 3,5,5-trimethyl-3-cyclohexene-1-one (beta-IP). The purity of the product beta-IP can reach 99.5-99.8wt%, and the reaction selectivity can reach 99.2-99.9%. The process has the advantages of small catalyst usage amount, high selectivity, avoidance of alkaline separation, less high-boiling residues and the like and a high-efficiency synthetic process.