The application discloses a natural alpha-
glucosidase inhibitor and a preparation method and application thereof, and the natural alpha-
glucosidase inhibitor is 3,3'-dimethoxy
ellagic acid extracted from a
sapium sebiferum. The application is specifically implemented according to the following steps: preparing a
sapium sebiferum extract; and separating and purifying the
sapium sebiferum extract to obtain 3,3'-dimethoxy
ellagic acid. The application obtains a novel natural alpha-
glucosidase inhibitor 3,3'-dimethoxy
ellagic acid, and the inhibition effect of the 3,3'-dimethoxy ellagic acid on alpha-glucosidase is obvious at a concentration of 4 mg / mL, so that the 3,3'-dimethoxy ellagic acid provides a
lead compound for research and development of a novel natural anti-diabetic
drug.