NOVELTY - Preparation of corilagin comprises taking coarse powder of Phyllanthus urinaria and adding to a carbon dioxide (CO2) supercritical extractor for obtaining extract; adding water for dissolving and filtering; absorbing filtering liquid by a macroporous absorption resin; collecting eluent; adjusting pH value to 4-4.5 by condensing liquid and acetic acid; using ethyl acetate-water mixed solvent for performing 6-10 levels counter current extraction; combining the extracting liquid; decompressing and recycling the solvent; and adding absolute ethyl alcohol for crystallizing.    USE - Preparation method of corilagin.    ADVANTAGE - The method has simple operation, small pollution and small energy consumption. The prepared corilagin has high product purity, and is easy to amplify industrialization.    DETAILED DESCRIPTION - Preparation of corilagin comprises: (A) taking coarse powder of P. urinaria and adding to CO2 supercritical extractor for obtaining the extract, where ethyl acetate is used as an entrainer, volume percentage of entrainer in the total extracting solvent is 3-8 (preferably 5)%, extracting pressure is 10-30 (preferably 20) MPa, temperature is 35-55 (preferably 45) degrees C, flow of CO2 is 1-3 (preferably 2) ml/g crude drug minute, and extracting time is 80-150 (preferably 100) minutes; (B) adding water for dissolving and filtering; absorbing the filtering liquid by a macroporous absorption resin; eluting with 20-60% of ethanol; collecting 3-8 times of eluent in column volume; decompressing, recycling and condensing the ethanol; and (C) adjusting the pH value to 4-4.5 by condensing liquid and acetic acid; using ethyl acetate-water mixed solvent at a ratio of 10:2 for performing 6-10 levels counter current extraction; combining the extracting liquid according to the volume ratio of condensing liquid to the mixed solvent of 1:6-10; decompressing and recycling the solvent; adding absolute ethyl alcohol for crystallizing; separating the crystallization; and washing and drying.