Objective To investigate the therapeutic effect of Metformin on Bleomycin induced pulmonary fibrosis. Methods Rat model of pulmonary fibrosis was established by inhalation of Bleomycin (with 24 successful rats model). Rats in control group (4 rats) received normal saline. Rats were administrated with Metformin, Prednisone or Pirfenidone 14 days after insults (6 for each group). No treatment was applied to rats in model group (6 rats). The pathological changes of lung tissue were observed by HE staining and Masson staining. Levels of TGF-beta and Hyp in bronchoalveolar lavage fluid and lung tissue were determined by ELISA. Results Rat model of Bleomycin induced pulmonary fibrosis was established successfully. HE staining and Masson staining suggested that Bleomycin induced pulmonary inflammation and fibrosis were mitigated by Metformin and Pirfenidone. Metformin and Pirfenidone inhibited the production of Hyp and TGF-beta. Prednisone exerted no obvious therapeutic effect on pulmonary fibrosis in late stage. Conclusions Metformin and Pirfenidone excluding Prednisone relieve advanced pulmonary fibrosis.