OBJECTIVE: To investigate the immunomodulatory mechanism by which Yangfei Huoxue decoction(YHD) alleviates bleomycin(BLM)-induced pulmonary fibrosis(PF) in rats.METHODS: Rats were randomly divided into two time-point groups(day 14 and 28), and each timepoint group comprised the following six subgroups: control, BLM, dexamethasone(DXM), YHD high dose(YHD-H), YHD middle dose(YHD-M), and YHD low dose(YHD-L). Haematoxylin and eosin and Masson staining, flow cytometry, enzymelinked immunosorbent assay, Western blotting and UPLC-QT of analyses were examined.RESULTS: The results showed that YHD reduced the degree of alveolar inflammation and fibrosis;downregulated the expression of CD28, CD80,CD86, Delta-like 1, Notch2, and Notch3; and upregulated the proportions of Th1/Th2 and Tc1/Tc2. The seven components of YHD were detected.CONCLUSION: The current study indicates that YHD mainly functions by regulating the immune system and that the molecular mechanism may be related to the regulation of the Notch signaling pathway.