The invention discloses a method for purifying roburic acid, which comprises the following steps: (1) taking the raw material large leaf gentian root, drying, pulverizing, soaking in an enzyme solution, carrying out water bath enzymolysis, and sufficiently stirring; (2) filtering, extracting the filter residue with 5-10 times of ethanol water solution 2-3 times, merging the extracting solutions, and concentrating under reduced pressure to obtain an extract; (3) passing the extract through macroporous adsorbent resin columns, eluting with ethanol water solution, and collecting the eluate; (4) recycling ethanol from the eluate under reduced pressure, extracting by ethyl acetate, concentrating the extracting liquid, passing the extracting liquid through silica gel columns, carrying out cyclohexane-ethanol gradient elution, carrying out TLC (thin layer chromatography) tracking and monitoring, and collecting the roburic acid fraction; and (5) concentrating the roburic acid fraction under reduced pressure to small volume, standing to crystallize, and carrying out methanol/petroleum ether-acetone ethanol recrystallization. The invention is simple to operate, has the advantages of high product yield and low cost, and is suitable for large-scale production.