To investigate the effect of compound essential oils (CEOs) on EndMT of mouse pulmonary vascular endothelial cells (MHC) induced by PM_2.5,and discuss the regulatory mechanism of CEOs by the TGF-β1/SMAD3/p-SMAD3 pathway.MHC cells were cultured in vitro.Design the PM_2.5 group (500 μg/mL),the CEOs group (PM_2.5 500 μg/mL + CEOs 10-5%),the inhibitor of TGF-β pathway SB431542 group (10 μmol/L) and the PM_2.5+SB431542 group (500 μg/mL + 10 μmol/L).The changes of cell viability and migration ability were analyzed by cell proliferation experiment and cell scratch experiment.RT-qPCR and Western blot were used to detect the levels of CDH5,CD31,Col1,Acta2,S100A4 and TGF-β signal pathway related factors.The cell viability of MHC began to increase after 36 h in the PM_2.5 group (P<0.000 1),and there is no significant difference in the CEOs group.The cell migration increased significantly in thePM_2.5 group,and CEOs can attenuate the effect of PM_2.5 on cell migration (36 h,P<0.05).The result of RT-qPCR and Western blot showed that the expression of EndMT related factors showed a positive trend with the prolongation of PM_2.5.CEOs had a beneficial intervention effect on EndMT induced by PM_2.5 exposure.Compared with the PM_2.5 group,Western blot showed that the expression of TGF-β1,TGF-βR1 and p-SMAD3 decreased in the CEOs group,and the expression of EndMT related factors was reversed after 48 h.CEOs ameliorates EndMT induced by PM_2.5,which is related to TGF-β1/SMAD3/p-SMAD3 pathway.