The invention relates to an aluminum electrolytic capacitor electrolyte and a preparation method thereof, wherein the electrolyte is prepared from the following raw materials in percentage by weight: 70% of glycol, 1.5% of ammonium dihydrogen phosphate, 8% of ammonium pentaborate, 14% of ammonium adipate, 4.5% of breakdown voltage enhancing agent, 1% of phosphorous acid and 1% of deionized water.The preparation method comprises the following steps: taking and adding 70kg of glycol and 1kg of deionized water into a container, uniformly stirring, and heating to 110 DEG C; weighing 4.5kg of breakdown voltage increasing agent, 1.5kg of ammonium dihydrogen phosphate, 1kg of phosphorous acid, 8kg of ammonium pentaborate and 14kg of ammonium adipate by using a scale, and then, sequentially adding the materials into the container and stirring; and keeping the mixture at the constant temperature of 110 DEG C for 30 minutes, naturally cooling the mixture to the room temperature, and then discharging. The invention has the advantages of enhancing the breakdown voltage of the electrolyte, improving the capacity of repairing aluminum foil oxidation films by oxygen ions of the electrolyte, reducing generation of water and precipitation of hydrogen gas in the working process, and obviously improving the service performance of the aluminum electrolytic capacitor.