Method for extracting Polygonum capitatum

The invention discloses a method for extracting Polygonum capitatum. The method comprises the following steps: (1) taking a dried product of Polygonum capitatum, performing cutting, adding 7 times theamount of water, performing heating to boiling, performing decocting for 1-2 h, and performing filtering to obtain a filtrate A; (2) adding 6 times the amount of water into a filter residue of the step (1), performing heating to boiling, performing decocting for 1-2 h, and performing filtering to obtain a filtrate B; (3) combining the filtrate A and the filtrate B, performing concentrating to a density of 0.4-0.8, and then performing cooling to room temperature to obtain a liquid medicine C; (4) adding ethanol into the liquid medicine C, performing even stirring, performing airtight refrigeration for 20-40 h, and then performing taking-out and filtering to obtain a filtrate D; and (5) heating and concentrating the filtrate D to obtain an extract of an extraction substance, and recoveringethanol. The method has th