An application using an active ingredient for preparing a pharmaceutical formulation. The pharmaceutical formulation is used for delaying the incidence and/or treatment of a pulmonary fibrosis. The active ingredient is selected from the following groups : a compound represented by formula (I), a pharmaceutically acceptable salt thereof, or a combination of the compound and the salt, wherein A is a five-carbon alkyl or alkenyl group comprising substituents listed in the following as required : -OH and =O; X is H or OH; Y is O; and if R1 is H or does not exist, then Y and A can form a bond to form a five-membered ring.