The invention relates to plant extracts, in particular to a preparation method of a rosemary extract. The preparation method comprises the following steps: picking rosemary leaves, and crushing into 30 to 80 meshes; adding crushed rosemary into a round-bottom flask, distilling and extracting rosemary essential oil, and pouring rosemary leaf residues into a blowing-type dehydrator, adjusting the temperature to 50 to 70 DEG C, and drying for 7 to 9 hours; after drying, adding the leaf residues into edible alcohol with the purity of 90 to 99 percent according to the solid-liquid ratio of 1 to 8, carrying out heating and extracting on a water bath pot with the temperature of 45 to 65 DEG C for 1.5 to 2.5 hours, collecting an extracting solution, extracting twice and then combining, wherein the extracting solution contains a rosemary water soluble extract and a liposoluble extract; recovering the alcohol in the extracting solution, then concentrating the extracting solution for carrying out Buchner funnel filtering, and pouring filtered residues into the dehydrator for drying, thus obtaining the rosemary liposoluble extract; carrying out concentrating and spray drying on the filtered filtrate to obtain a rosemary water soluble extract. The preparation method of the rosemary extract, disclosed by the invention, has the advantages that work efficiency is improved and the cost is reduced.