Objective To study the mechanism of Souti Feiluo Formula（formula to treat pulmonary fibrosis）for pulmonary fibrosis.Methods Totally 128rats were randomized into the sham operation group

model group

Chinese medication group and western medication group

with 32in each.The pulmonary fibrosis models were established by intratracheal instillation of bleomycin in each group except the sham operation group.The sham operation group was given intratracheal instillation of normal saline.At the 24th hour after modeling

the Chinese medication group was gavaged with 0.68g/（kg·d）Souti Feiluo Formula

the western medication group was gavaged with 5mg/（kg·d）prednisolone and the model group and sham operation group were gavaged with same amount of deionized water.The rats were sacrificed on the 7th

14th

28th and 45th day

respectively.The lung tissues were taken for pathological observation of the degree of pulmonary alveolitis and fibrosis.The content of transforming growth factor-β1（TGF-β1）and the expressions of Smad3and Smad7were detected.Results Comparing with the model group

the degree of alveolitis was significantly decreased on the 7th

14th and 45th day（P<0.05）and the degree of pulmonary fibrosis was significantly decreased on the 7th and 45th day（P<0.05）in the Chinese medication group and western medication group.There was no significant difference between the model group

Chinese medication group and western medication groups in the content of TGF-β1（P>0.05）.Comparing with the model group

the expression of Smad3 was significantly decreased in the Chinese medication and western medication groups（P<0.05）on each of point-in-time

especially in the Chinese medication group（P<0.05）.Comparing with the model group

the expression of Smad7was significantly increased in the Chinese medication and western medication groups on each of point-in-time（P<0.05）.Conclusion Souti Feiluo Formula can inhibit the pulmonary fibrosis caused by bleomycin and its mechanism may be relevant to regulating the expression of Smad.