The invention relates to a method for preparing silybin. The method comprises the following process steps: crushing silybin seeds into 20 to 40 meshes, and degreasing the crushed silybin seeds thrice by using n-hexane; refluxing and extracting degreased coarse materials by using dilute ethanol; concentrating the extract under reduced pressure till the extract has no ethanol smell, extracting the concentrate by using ethyl acetate, stirring and drying ester phase and silica gel, then injecting a dried product to a column, eluting the dried product by using benzene or benzene-ethyl acetate, collecting the elute by sections, combining the elute to obtain main elute component of the silybin, concentrating the elute under reduced pressure, dissolving the elute in ethanol solution, adding active carbon into the solution, stirring the solution, decolorizing the solution for 0.5 to 1 hour, filtering the active carbon from the decolorized solution, concentrating the decolorized solution under reduced pressure to 40 to 60 percent of the primary volume, cooling the concentrate to separate out crystals, crystallizing the crystals by using hot ethanol, and repeating the crystallization step for 2 to 4 times to obtain the silybin. The method for producing the silybin has the advantages of simple process, low solvent toxicity, low production cost, and easy realization of industrialization.