The invention provides novel applications of thyroid hormone, and pharmaceutically acceptable salts or prodrugs of thyroid hormone. According to the invention, thyroid hormone, and the pharmaceutically acceptable salts or prodrugs of thyroid hormone can be used for treating and / or preventing pulmonary diseases; thyroid hormone and the pharmaceutically acceptable salts or prodrugs of thyroid hormone can be used for protecting alveolar epithelial cells effectively, adjusting surface protein synthesis, storage, and distribution of alveolar epithelial cells, promoting maturation, differentiation, and cell integrity of alveolar epithelial cells, promoting repairing of damaged mitochondria in alveolar epithelial cells, improving mitochondria biosynthesis, preventing and reversing pulmonary fibrosis, adjusting immunity reaction, changing cancerous environment, treating and preventing pulmonary diseases, improving pulmonary functions such as gas exchange, and achieving treatment effect, and are beneficial for cleaning of pulmonary effusion and repairing of damaged lung tissue.