Objective: To explore the formation mechanism of benign biliary stricture. Methods: A model of trauma of common bile duct was established in 28 dogs and then repaired. The anasomosis tissues were taken on the 1st week, 3rd week and the 3rd month, 6th month respectively after operation and examined by using light microscopy and electromicroscopy. Macrophage, TGF-β1 and α-SMA were studied immunohistochemically. Results: The mucosal epithelium of common bile duct restored poorly, chronic inflammation lasted for a long time, fibroblasts proliferated actively, extracellular matrix overdeposited; and myofibroblasts functioned actively and existed during the whole healing process. Immunohistochemical test showed a high expression of macrophage, TGF-β1 and α-SMA during healing process lasting a long duration. Macrophages were found in the lamina propria under mucosa, TGF-β1 in the granulation tissue, fibroblasts and endothelial cells of blood vesssels, while α-SMA in the myofiroblasts and smooth muscle tissue. Conclusion: The healing of bile duct is in the mode of overhealing. Myofibroblast is the main cause for contracture of scar and stricture of bile duct. The high expression of macrophage, TGF-β1 and α-SMA is closely related to active proliferation of fibroblasts, extracelluar matrix overdeposition and scar contracture of bile duct.