OBJECTIVE To investigate the mechanism of Yangfei tongluo formula in delaying airway remodeling in post-infectious bronchiolitis obliterans （PIBO） model rats.METHODS Forty-eight 2-week-old SPF male SD rats were randomly divided into control group （Control group）， PIBO model group （Model group）， Prednisone Acetate tablets+Azithromycin tablets group [positive control group， Prednisone Acetate tablets 0.006 3 g/（kg·d）+Azithromycin tablets 0.031 5 g/（kg·d）]， and high-， medium-， and low-dose Yangfei tongluo formula groups [42.42， 21.21， 10.60 g/（kg·d）]. The PIBO rat model was established by intratracheal instillation of diacetyl. After modeling， rats in each group were administered corresponding drug solution or distilled water by gavage once daily for 21 consecutive days. Hematoxylin-eosin staining was used to evaluate the pathological changes of lung tissue， and Masson staining was used to assess the degree of pulmonary fibrosis. Western blot and real-time quantitative PCR were performed to detect the protein and mRNA expression levels of epithelial-mesenchymal transition （EMT）-related markers [E-cadherin， N-cadherin， α -smooth muscle actin （ α -SMA）， Vimentin] and transcription factors [snail homolog 1（Drosophila）-like 1 protein （Snail1）， zinc finger E-box-binding homeobox protein 1 （ZEB1）， Twist-related protein 1 （Twist1）] in lung tissue. ELISA was used to detect the levels of transforming growth factor-β 1 （TGF-β 1 ） and vascular endothelial growth factor （VEGF） in blood and bronchoalveolar lavage fluid.RESULTS Compared with the Control group， the lung tissues of rats in the Model group showed extensive destruction of alveolar structure and massive inflammatory cell infiltration in the interstitium. The protein and mRNA expression levels of E-cadherin were significantly decreased， while the protein and mRNA expression levels of N-cadherin， Vimentin， α -SMA， Snail1， ZEB1， and Twist1， as well as the collagen-positive area and the levels of TGF-β 1 and VEGF， were significantly increased （ P ＜0.05）. Compared with the Model group， the pathological injury of lung tissue in each administration group was significantly improved， and the above indicators （except collagen-positive area） were significantly reversed （ P ＜0.05）.CONCLUSIONS Yangfei tongluo formula may delay airway remodeling in PIBO by regulating the TGF-β 1 /VEGF-mediated signaling network and inhibiting the activation of EMT-related transcription factors， thereby blocking the EMT process.