NOVELTY - Extracting refined astragaloside IV from Astragalus membranaceus comprises performing ethanol reflux extraction to A. membranaceus decoction pieces, filtering, concentrating filtrate, extracting with sodium hydroxide solution to obtain alkali hydrolyzate, passing into macroporous resin column, eluting with e.g. sodium hydroxide solution and ethanol, collecting eluate to obtain a purified solution, purifying via weakly alkaline anion exchange resin bed, collecting eluate, concentrating, filtering, dissolving filter cake in distilled water, lyophilizing and recrystallizing.    USE - The method is useful for extracting refined astragaloside IV from Astragalus membranaceus.    ADVANTAGE - The method carries out efficient extraction, separation and purification by ethanol reflux extraction, alkali hydrolysis, impurity removal by macroporous resin, decolorization by ion exchange, and recrystallization to obtain white product with yield of more than 0.07%, and purity of more than 99%; and is simple, feasible, free from pollution and suitable for industrial production.    DETAILED DESCRIPTION - Extracting refined astragaloside IV from Astragalus membranaceus comprises (a) weighing A. membranaceus decoction pieces, 60-80% adding ethanol solution (6-12 times), heating, performing reflux extraction for 2-3 times with each time for 1-3 hours, soaking for 20-40 minutes for the first time, filtering, combining the extracted filtrates, depressurizing and concentrating until there is no alcohol smell, achieving a constant volume until the volume-weight ratio of the medicine liquid to medicine material is 1:1-2:1 to obtain a concentrated liquid, (b) adding the concentrated liquid into an extraction kettle, adding 1 mol/l sodium hydroxide solution where 1 g of the medicine material is added with 0.005-0.02 g of sodium hydroxide, heating to 60-100 degrees C, stirring, continuously refluxing for 2-6 hours, diluting with distilled water to 0.04-0.4 g medicine material/ml to obtain alkali hydrolyzate, (c) weighing macroporous resin by controlling the weight ratio of the medicine material to the resin to be 2:1-1:2, filling the resin into a chromatographic column with a height-diameter ratio of 1:3-1:12, washing with 95% ethanol and distilled water, loading the alkali hydrolyzate, controlling the adsorption flow rate to be 6 times of the column volume/hour, saturating for 1-3 hours, eluting with 10-20 column volume times of the distilled water to remove sugar, controlling the elution flow rate to be 12 times of the column volume/hour, removing impurities by 10-20 column volume times of 0.1 mol/l sodium hydroxide solution, controlling the elution flow rate to be 12 times of the column volume/hour, rinsing with distilled water to a neutral state, removing the impurities by 7 column volume times of 40% ethanol solution, controlling the elution flow rate to be 12 times of the column volume per hour, eluting with 10-20 column volume times of 60% ethanol, controlling the elution flow rate to be 12 times of the column volume per hour, collecting the solution eluted by 60% ethanol solution to obtain purified solution A, (d) weighing weakly alkaline anion exchange resin by controlling the weigh ratio of the medicine material to the resin to be 3.2:1-1:1, filling into a chromatographic column with a height to diameter ratio of 1:3-1:10, treating the weakly alkaline anion exchange resin with acid and alkali, rinsing with distilled water until the pH is 7, passing the purified solution A through the weakly alkaline anion exchange resin bed, controlling the flow rate to be 3.6 times of the column volume per hour, collecting the eluate, eluting with 3-5 column volume times of 60% ethanol solution, collecting the eluate, combining the two eluates, concentrating to 6.4-16 g of the medicine material/ml to obtain purified solution B, and (e) placing the purified solution B in a refrigerator for three days, filtering, dissolving the filter cake with distilled water and lyophilizing, placing the lyophilized sample in a vacuum dryer to dry, recrystallizing with 95% ethanol.