The invention discloses a preparation method of an olive leaf extract. The preparation method comprises the following steps: a, selecting olive leaves; b, putting the selected olive leaves into saline water, and soaking for 1-2 hours; c, drying; d, after drying, grinding into fine powder; e, adding 3-8 times of water into the raw material, and then adding cellulase; f, after enzymatic hydrolysis, filtering to obtain an enzymatic hydrolysate; g, directly enabling the enzymatic hydrolysate to pass through a neutral aluminum oxide column with the diameter-height ratio of 1:4 to 1:13, eluting for removing impurities by using water and an ethanol solution with the concentration of 90% respectively, eluting by using a mixture of glacial acetic acid with the concentration of 0.2-0.5% and an ethanol solution with the concentration of 45%, and collecting an eluate, wherein the volume of water is 2-3 times of the column volume, the volume of the ethanol solution with the concentration of 90% is 0.8-1.5 times of the column volume, and the volume of the mixture is 7-9 times of the column volume; h, volatilizing the glacial acetic acid and the ethanol in the eluate, and performing microwave vacuum drying to obtain the olive leaf extract. By the preparation method, active components can be dissolved out more effectively, and energy consumption in the extraction process is greatly reduced and thus the production cost is reduced.