The invention relates to a preparation method of longan extract. The preparation method adopts a pectase and cellulase simultaneous enzymolysis extraction method. The preparation method comprises thefollowing steps: drying fresh longan with hot air of 80 DEG C, removing peels and kernels, obtaining dried longan pulp, adding deionized water, soaking for 12h, wherein a material-to-water ratio is 1:3, and mashing by using a high-speed tissue mashing machine; adding deionized water into a mashed matter, wherein a material-to-water ratio is 1:12, simultaneously enzymolysing by adopting pectase andcellulase, wherein by calculating according to a weight percentage, the consumption of pectase is 0.6 percent, the consumption of cellulase is 0.05 percent, adjusting a pH value to be 3.1, the enzymolysis temperature is 52 DEG C, the enzymolysis time is 160 min, after the enzymolysis is ended, deactivating the enzyme for 30min at 90 DEG C, filtering for 200 meshes, collecting filtrate, concentrating the filtrate into half-flowing pulp, dissolving the pulp into the deionized water according to a volume ratio of 1:10, stirring, uniformly shaking, thus obtaining the longan extract.