NOVELTY - Extracting astragaloside IV from Astragalus mongholicus, by (a) crushing radix astragali, adding water, reflowing and extracting the mixture, concentrating and adding ethanol, centrifuging, precipitating and collecting supernatant, (b) concentrating the supernatant, adding alkaline solution, reacting and extracting product using n-butanol, collecting and concentrating organic phase, and (c) adding ethyl acetate, collecting and concentrating the water phase, filtering and washing the filter cake, and adding methanol and re-crystallizing product.    USE - The method is useful for extracting high purity astragaloside IV from A.mongholicus (claimed), which is used in medicine.    ADVANTAGE - The method is simple and environmentally-friendly, produces astragaloside IV with improved yield of more than 0.08% and purity of more than 98% and without chemical residues, and is suitable for large-scale industrial production.    DETAILED DESCRIPTION - Method for extracting high purity astragaloside IV from Astragalus mongholicus, involves (a) obtaining and crushing radix astragali, adding 10-15 times of water to the crushed radix astragali, reflowing and extracting the obtained mixture for 2-4 times, where each time for 1-1.5 hours, combining the extracts, concentrating the obtained mixture to thick paste with relative density of 1.2-1.3, adding ethanol to the concentrated product to make the ethanol content to 60-80 %mass, fully stirring the obtained mixture, centrifuging the mixture, and precipitating and collecting supernatant, (b) concentrating the supernatant until the relative density is 1.05-1.2, adding the concentrated product into a reaction kettle, adding alkaline solution to the kettle, adjusting pH value to 9-10, reacting the mixture at 40-50 degrees C for 8-12 hours, adjusting the pH value to neutral, extracting the obtained product using n-butanol, collecting the organic phase, and concentrating the organic phase to relative density of 1.1-1.2, and (c) adding ethyl acetate to the concentrated product, collecting water phase, concentrating the water phase to relative density of more than 1.3, and standing to precipitate, filtering the obtained product, washing the filter cake using water, and adding methanol and re-crystallizing to obtain the astragaloside IV.