NOVELTY - Extracting and preparing high-purity silibinin from Polygonum capitatum herb, comprises: (a) preparing Polygonum capitatum flow extract: heating, refluxing and extracting crude Polygonum capitatum herb powder for 1-3 times by 5 volume times of petroleum ether, and then abandoning extracted liquid; and then soaking by 2 volume times of aqueous ethanol solution with the volume concentration of 80-90%; percolating or heating, refluxing and extracting by 5 volume times for 1-3 times; (b) preparing crude silibinin extract; and (c) preparing high-purity silibinin.    USE - The method is useful for extracting and preparing high-purity silibinin from Polygonum capitatum herb (claimed).    ADVANTAGE - The invention initially discovers and optimizes the method for extracting and preparing the high-purity silibinin from the Polygonum capitatum herb, and is free from poison, friendly to environment, free from environmental pollution, simple in operation and low in cost with high yield and purity of the silibinin, suitable for promotion.    DETAILED DESCRIPTION - Extracting and preparing high-purity silibinin from Polygonum capitatum herb, comprises: (a) preparing Polygonum capitatum flow extract: heating, refluxing and extracting crude Polygonum capitatum herb powder for 1-3 times by 5 volume times of petroleum ether, and then abandoning extracted liquid; and then soaking by 2 volume times of aqueous ethanol solution with the volume concentration of 80-90%; percolating by 20 volume times or heating, refluxing and extracting by 5 volume times for 1-3 times, and then depressurizing and concentrating till there is no alcohol smell to obtain the Polygonum capitatum flow extract; (b) preparing crude silibinin extract: adding 3-4 volume times of water to the Polygonum capitatum flow extract for mixing and suspending, extracting by 10 volume times of ethyl acetate; depressurizing, concentrating and evaporating the extract liquid and then performing silica gel column chromatograph; eluting by elution solution of the petroleum ether and the ethyl acetate on ratio of 2:1 to remove weakly polar impurities; and then eluting by the elution solution of the petroleum ether and the ethyl acetate on ratio of 1:1; depressurizing, concentrating and evaporating the eluted liquid to obtain light green crude silibinin; and (c) preparing high-purity silibinin: performing the silica gel column chromatograph to the light green crude silibinin again, eluting by the elution solution of the petroleum ether and the ethyl acetate on ratio of 2:1 to remove other impurities such as flavone lignin, ethyl gallate and quercetin; and then eluting by the elution solution of the petroleum ether and the ethyl acetate on ratio of 1:1, so that light green silibinin powder is crystallized in the depressurizing and concentrating process of the eluted liquid; filtering, washing and recrystallizing to obtain white silibinin powder with the purity higher than 98%, where the temperature in the process of depressurizing and concentrating the extracted liquid, the extract liquid or the eluted liquid is not higher than 65 degrees C.