Objective To explore the effects and mechanisms of metformin (Met) on proliferation and osteogenic differentiation of bone marrow stem cells (BMSCs) in type 2 diabetes mellitus (T2DM) rats exposed to micro arc oxidation of hydroxyapatite (MAO-HA) coated Titanium. Methods High sugar and high-fat diet (fed for 4 weeks) combined with intraperitoneal injection of streptozotocin (STZ) (50 mg/kg) was used to establish T2DM rat model. Rats were randomly divided into Normal group, T2DM group, low-dose metformin group and high-dose metformin group. Metformin group rats were treated with metformin (150 mg/kg/d, 300 mg/kg/d) by gavage. After 4 weeks of lavage, rats were euthanized and BMSCs were separated from the femur and tibia. Electrochemical method (ELC) and micro arc oxidation method (MAO) were used to prepare hydroxyapatite (HA) coated titanium metal materials. BMSCs from normal rat were implanted on the surface of ELC-HA and MAO-HA coatings. After 48 hours of cultivation, scanning electron microscopy was used to observe the surface morphology of the coating and the adsorption of BMSCs on its surface. BMSCs from different sources were implanted on the surface of MAO-HA coating and divided into NC group, T2DM group, Met-Low group and Met-High group. After 48 hours of cultivation, CCK-8 and EdU staining were used to detect the proliferation ability of BMSCs; Alkaline phosphatase (ALP) staining and Alizarin red staining were used to detect the osteogenic differentiation ability of BMSCs; Western blot was used to detect proliferation related markers ［proliferating cell nucleus antigen (PCNA), Ki67］, osteogenic differentiation related markers ［ALP, osteocalcin (OCN), osteopontin (OPN)］, Wnt/β catenin pathway related proteins ［Wnt3a, β Catenin, glycogen synthase Kinase-3β (GSK-3β)］ protein levels. Results The surface of MAO-HA coating had uniformly rough pores, on which BMSCs were fully extended and cell protrusions were coarse, while the surface of the ELC-HA coating was very smooth, with BMSCs wrinkled and protrusions finer on it. Compared with NC group, the survival rate, EdU positive cell rate and osteogenic differentiation ability of BMSCs in T2DM group were significantly decreased; PCNA, Ki67, ALP, OCN, OPN, Wnt3a, β catenin protein levels were significantly decreased, GSK-3β protein level was significantly increased (all P＜0.05). Compared with T2DM group, the survival rate, EdU positive cell rate and osteogenic differentiation ability of BMSCs in Met-Low group and Met-High group were significantly increased; PCNA, Ki67, ALP, OCN, OPN, Wnt3a, β catenin protein levels were significantly increased, GSK-3β protein level was significantly decreased (all P＜0.05). Conclusion Metformin can promote the proliferation and osteogenic differentiation ability of BMSCs on MAO-HA titanium surface in T2DM rats, which may be play a role in activating Wnt/βcatenin pathway