NOVELTY - Preparing high purity astragaloside IV comprises (1) adding radix astragali with 12 times of water to extract and then separating and collecting the extracting solution, water, repeating extract preparation, combining the extracting solutions, (2) concentrating the extracting liquid and then heating to 20-60 degrees C for 8-14 hours and then adding alkali solution to adjust the pH value, and (3) adding defoaming agent with the extract liquid and then slowly stirring, standing to lost foam and then adding flocculating agent and water and stirring the mixture to settle suspension impurity.    USE - The method is useful for preparing high purity astragaloside IV (claimed).    ADVANTAGE - The method prepares the high purity astragaloside IV in a simple, eco-friendly and cost effective manner with high yield rate and without resin blockage and damaging a filter membrane.    DETAILED DESCRIPTION - Preparing high purity astragaloside IV comprises (1) adding radix astragali with 12 times of water to extract and then separating and collecting the extracting solution, water, repeating extract preparation for 2-3 times combining the extracting solutions, (2) concentrating the extracting liquid and then heating to 20-60 degrees C for 8-14 hours and then adding alkali solution to adjust the pH value to 1-14, (3) adding defoaming agent (0.0001-0.0005%) with the extract liquid and then slowly stirring for 10-60 minutes, standing to lost foam and then adding flocculating agent (0.001-0.005%) and water and stirring the mixture for 10-60 minutes and then standing for 6-10 hours to settle suspension impurity, separating an upper-layer clear liquid and film filtering to obtain liquid medicine, (4) adjusting the pH value of liquid medicine to 6.5-8, (5) separating the medicine liquid by macro-porous resin column and then eluting with de-ionized water, to collect low concentration and high concentration ethanol and eluent, (6) concentrating the eluent to remove high-concentration ethanol to obtain concentrated solution, (7) refining the concentrated liquid by water and then by water saturated n-butyl alcohol, extracting an organic solution layer A, washing the layer A using dilute alkali solution for 2-3 times, collecting the organic solution layer B, washing the layer B by distilled water for 2-3 times, collecting a organic solution layer C, distilling and concentrating the organic solution layer C to obtain a white crystal and then cooling and crystallizing by adding crystallizing material, filtering the obtained product, washing the crystal using three-distilled water to obtain a white astragaloside IV, and (8) drying the white astragaloside IV at 115-120 degrees C for 8-10 hours and then vacuum drying at 50-60 degrees C for 20-24 hours to obtain with the white astragaloside IV with purity of more than 99.5%.