NOVELTY - Method for extracting resveratrol from giant knotweed, involves taking rhizome of giant knotweed raw material as raw material, crushing, sieving, adding acetic acid sodium acetate buffer, reacting, adding cellulose, performing enzymolysis, filtering, processing the solid residue, collecting extract, concentrating, combining concentrated extracts and obtained filtrate to obtain a crude liquid, passing through macroporous resin column, fractionating, concentrating, performing chromatographic separation, purifying, decoloring, and freeze-drying to obtain crystalline powder.    USE - The method is useful for extracting resveratrol from giant knotweed which is used as medicine for preventing cardiovascular disease and liver cancer and as skincare cosmetic.    ADVANTAGE - The method is environmentally-friendly, performed simply and cost-effectively in short period of time with high purity of 98.31% and suitable for industrial popularization, and provides high yield of up to 1.40%.    DETAILED DESCRIPTION - Method for extracting resveratrol from giant knotweed, involves (a) taking giant knotweed raw material as raw material, placing the rhizome of giant knotweed in a crusher, crushing, sieving the crushed rhizome through sieve of 240-320 mesh size, collecting sieved powder, adding acetic acid sodium acetate buffer to the powder in a volume ratio of 1 g:(1-10) mg:(10-50) ml, regulating pH using hydrochloric acid or sodium hydroxide solution to 4-6, placing in a batch reactor, reacting at 30-60 degrees C and 80-200 revolutions/minute (rpm), stirring for 15-30 minutes, adding cellulose, and performing enzymolysis by maintaining the temperature at 30-60 degrees C, mixing and reacting solid-liquid mixture for 15-30 hours, (b) placing processed solid-liquid mixture in a filter press for solid-liquid separation, collecting filtrate and solid residue, mixing the solid residue with 50-75% methanol in a volume ratio of 1 g:(5-20) ml, placing mixture in a extraction tank at 35-65 degrees C under the condition of stirring at 80-200 rpm for 15-60 minutes, passing through secondary filter, collecting extract and solid residue (I), again mixing the solid residue (I) and methanol, placing mixture in a extraction tank at 35-65 degrees C under the condition of stirring at 80-200 rpm for 15-60 minutes, filtering, collecting extract (I) and solid residue (II), repeating for 1-3 times, combining the extracts, concentrating by placing in a concentrator until there is no alcohol odor, collecting concentrated extract, evaporating solvent, and combining concentrated extracts and obtained filtrate to obtain a crude liquid, and (c) mixing the crude liquid with macroporous resin in a volume ratio of 1 g:1-10 ml, passing through macroporous resin column by pumping at constant-current of 1-3 BV, fractionating using 10-20% ethanol solution, where flow rate is 1-3 BV/hour, separating, washing, separating wash liquid, passing the wash liquid at flow rate of 1-3 BV/hour through the column, collecting liquid, passing distilled water at 2-5 BV with flow rate of 1-3 BV/hour, collecting first eluate, passing using 20-30% ethanol with flow rate of 1-3 BV/hour, collecting second eluate, combining eluates, concentrating to obtain concentrated liquid, mixing the concentrated liquid with neutral aluminum oxide in a volume ratio of 1 g:10-20 ml, passing through chromatographic column at 1-3 BV/hour, performing chromatographic separation using 60-80% ethanol, washing, purifying, decoloring by adding activated carbon and stirring for 1-5 hours at room temperature, filtering, concentrating, pre-freeze-drying at -10 degrees C to -18 degrees C and 20-60 Pa for 2-3 hours, and freeze-drying at -40 degrees C to -60 degrees C for 24-30 hours to obtain product.