Our study points out that the mechanism of CAT protecting against pulmonary fibrosis induced by BLM in mice is related to the regulation of TGF-β1, Smad2, Smad3, Ang II, AT1, E-cadherin, N-cadherin and α-SMA as well as the phosphorylation of Smad2 and Smad3, also it is given orally which makes it easier to put into clinical practice. The gene discussed is CAT; the disease is pulmonary fibrosis.