The invention relates to application of icaritin to the preparation of medicine for preventing or treating pulmonary fibrosis and belongs to the field of medicine. The icaritin is traditional Chinese medicine monomer extracted from traditional Chinese medicine epimedium. Animal experiments show that the icaritin has evident preventing and treating effects on the pulmonary fibrosis. The icaritin is definite in curative effect on the pulmonary fibrosis, low in side effect and promising in medical application prospect.