The present invention relates to a method of delaying the onset of pulmonary fibrosis or treating pulmonary fibrosis, comprising administering to a subject in need an effective amount of an active ingredient selected from the group consisting of a compound of formula (I), a pharmaceutically acceptable salt of the compound of formula (I), and combinations thereof:wherein,A is a C5 alkyl or alkenyl optionally substituted with —OH or ═O；X is H or OH；Y is O； andR1 is H or absent, with the proviso that, when R1 is absent, Y and A bind together to form a five-membered ring.
