The medicine for treating flat wart is prepared with bezoar 100 weight portions, honeysuckle flower 5-15 weight portions, isatis root 4-16 weight portions or isatis leaf 8-32 weight portions, coix seed 5-15 weight portions, and solvent alcohol or white vinegar 100-180 weight portions. The materials may further include forsythia, mint, Chinese goldthread and other three Chinese medicinal materialsin certain weight proportion. The preparation process includes the following steps: crushing the Chinese medicinal materials except bezoar into meal, soaking and percolating the meal and collecting percolate, grinding bezoar into fine powder and adding into the percolate via stirring, concentrating to obtain the medicine. The present invention is used to treat flat wart through external application.