Objective To investigate the effect of targeted inhibition of DNA methyltransferase 1 (DNMT1) on transforming growth factor β1 (TGF-β1) -induced cardiac fibroblast (CFs) fibrosis and its mechanism. 〖WTHZ〗Methods Recombinant lentivirus with DNMT1 siRNA was used to transfect CFs, qRT-PCR and Western blot were used to detect the expression of DNMT1 in CFs after transfection. The experiment was divided into control group, TGF-β1 group, si-NC+TGF-β1 group, si-DNMT1+TGF-β1 group, si-DNMT1+TGF-β1+3-methyladenine (3-MA) group, the proliferative activity of CFs was determined by CCK-8 method, the migration number of CFs was detected by Transwell method, the expression of α-smooth muscle actin (α-SMA) was detected by immunofluorescence staining, the protein expression of collagen type I (COL Ⅰ), collagen type Ⅲ (COL Ⅲ), fibronectin (FN), microtubule associated protein light chain 3 (LC3) and Beclin1 were detected by Western blot. 〖WTHZ〗Results The relative expression of DNMT1 mRNA and protein in CFs infected with DNMT1 siRNA recombinant lentivirus were significantly down-regulated (P＜0.05). Compared with TGF-β1 group, cell proliferation activity in si-DNMT1+TGF-β1 group was significantly decreased (P＜0.05), the number of cell migration was significantly decreased (P＜0.05), and the relative fluorescence intensity of α-SMA was significantly decreased (P＜0.05), the relative protein expressions of COLⅠ, COL Ⅲ and FN were significantly down-regulated (P＜0.05), while the ratio of LC3-Ⅱ/LC3-Ⅰ protein and the relative protein expression of Beclin1 were significantly up-regulated (P＜0.05). However, after the addition of autophagy inhibitor 3-MA in si-DNMT1+TGF-β1 group, there was no significant change in cell proliferation activity (P＞0.05), but the number of cell migration was significantly increased (P＜0.05), the relative fluorescence intensity of α-SMA was significantly increased (P＜0.05), and the relative protein expressions of COL Ⅰ, COL Ⅲ and FN were significantly up-regulated (P＜0.05), the ratio of LC3-Ⅱ/LC3-Ⅰ protein and the relative protein expression of Beclin1 were significantly decreased (P＜0.05). Conclusion Targeted inhibition of DNMT1 can improve the abnormal proliferation and migration of CFs induced by TGF-β1 and inhibit fibrosis, which may be related to the promotion of autophagy