ETHNOPHARMACOLOGICAL RELEVANCE: The Da-Yuan-Yin (DYY) decoction, a classical multi-herbal preparation documented in the Treatise on Pestilence (Wen Yi Lun,⟪⟫), exhibits therapeutic potential in respiratory pathophysiology. Clinical studies during the COVID-19 pandemic have validated DYY's therapeutic efficacy in ameliorating respiratory symptoms in patients. However, its pharmacological mechanisms against lung injury remain unexplored. AIM OF THE STUDY: This investigation sought to delineate the medicinal efficacy and underlying pharmacological mechanisms of DYY through integrated experimental models encompassing animal studies and cellular assays. MATERIALS AND METHODS: Pharmacological evaluation was conducted in a mouse model of pulmonary injury via intratracheal (i.t.) administration of bleomycin (BLM). Test cohorts received DYY extract at graded concentrations: low-dose (4.3 g/kg), medium-dose (8.6 g/kg), and high-dose (17.2 g/kg) via daily oral gavage. After 14 consecutive days of intervention, pulmonary specimens were harvested. Histomorphological alterations were quantified through Hematoxylin-eosin and Masson trichrome staining of pulmonary parenchyma. E-cadherin and α-SMA protein distribution in tissue samples was monitored by immunohistochemical or immunofluorescent staining techniques. Longitudinal fibrosis progression was assessed through HYP quantification on day 21 following BLM instillation. TGF-β1-elicited epithelial-mesenchymal transition (EMT) in A549 alveolar epithelial cells served as an in vitro paradigm. Proteomic characterization of EMT markers (E-cadherin, vimentin, N-cadherin, α-SMA) was conducted via immunoblotting. Migratory capacity was evaluated using standardized scratch assay protocols. Transcriptional dynamics of EMT-associated genes (CDH1, CDH2, VIM, ACTA2) were monitored by RT-qPCR. Subcellular β-catenin redistribution was visualized through confocal microscopy following fluorescence labeling. RESULTS: Histopathological analysis of day 14 specimens revealed that DYY intervention attenuated pulmonary histoarchitectural disruption, preserved epithelial integrity through E-cadherin maintenance, and suppressed α-SMA-mediated mesenchymal activation. Longitudinal evaluation at day 21 demonstrated DYY-mediated significant attenuation of fibrotic progression, evidenced by the reduction in HYP accumulation (p < 0.01) and collagen deposition regression. In cell-based models, DYY treatment upregulated CDH1 transcript/protein levels (p < 0.01) while downregulating mesenchymal markers (N-cadherin; vimentin; α-SMA; p < 0.05). Scratch-wound assays demonstrated that DYY treatment significantly suppressed TGF-β1-induced migration of A549 cells (p < 0.01). Mechanistically, DYY disrupted β-catenin nuclear localization, reducing transcriptionally active β-catenin in cytoplasmic fractions. Crucially, in vivo validation confirmed DYY's dose-dependent inhibition of EMT progression. CONCLUSIONS: This study delineates a molecular cascade through which DYY exerts its therapeutic effects: CDH1 transcriptional upregulation mechanistically mediates E-cadherin/β-catenin complex reconstitution at adherens junctions, achieving restoration of membrane-localized β-catenin. This stabilization effectively blocks β-catenin nuclear translocation, thereby suppressing α-SMA transcriptional activation. Crucially, early DYY intervention demonstrated alveolar epithelial preservation and significant attenuation of fibrotic progression, positioning it as a multi-target therapeutic strategy against EMT-driven pulmonary pathologies. This study demonstrates DYY's efficacy in mitigating bleomycin-induced alveolar injury within a single GMP-certified production batch; however, systematic validation of its long-term pharmacological stability under variable environmental conditions and multi-batch reproducibility remains necessary to confirm clinical translatability.