The invention relates to a method for synthesizing azelaic acid through single ionic liquid catalyzing oleic acid. The method comprises the following steps: oleic acid and a 1-(alpha-acid) methyl-3-methylimidazole phosphotungstic acid ionic liquid catalyst are mixed, then a hydrogen peroxide solution is added, the mixture is fully stirred, after the reaction, an oil layer is on the upper layer, a water lay is on the lower layer, and separation is easy; a separated aqueous phase is refrigerated and crystallized, white powder is precipitated, and azelaic acid solid is obtained through suction filtration and drying. According to the method, other chemical apparatuses are not required to be added in the whole reaction process, energy is saved, the reaction speed is accelerated, the time is saved, and no large number of organic solvent is required in the reaction, so that the method is green and environment-friendly. The method for synthesizing azelaic acid through single ionic liquid catalyzing oleic acid has the advantages that the reaction yield is high, one step reaction process is simple, the reaction system is easy to separated, the production cost is effectively reduced, and environment is protected.