The invention relates to a drug composition for treating hepatitis C infection and a unit dosage form. The drug composition and the unit dosage are prepared from KW136(N-[(2S)-1-[(2S)-2-{4-[7-(4-{2-[(2S)-1-[(2S)-2-(methoxycarbonyl)amino]3-methylbutyryl]pyrrolidine-2-yl)-1H-imidazole-4-yl}phenyl}-2H-1,3-benzodioxole-4-yl]-1H-imidazole-2-yl}pyrrolidine-1-yl]-3-methyl-1-oxobutane-2-yl]methyl carbamate dihydrochloride, a compound as shown in a formula (II) and at least one pharmaceutically acceptable excipient which are in therapeutically effective amounts. The invention also discloses a method for preparing the drug composition and the unit dosage form.