The osteogenic activity and mechanical properties of the bone repair scaffold are important for its clinical application. Mg-M/HT porous composite scaffold was prepared with hardystonite (Ca2ZnSi2O7, HT) with good mechanical properties as a matrix and Mg-doped biodegradable mesoporous bioactive glass (MBG) as a coating. The effect of Mg doping on the microstructure and osteogenic activity of the M/HT composite scaffold was investigated. The microstructures of the composite scaffolds were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The osteogenic activity of the scaffolds was investigated with human bone marrow mesenchymal stem cells (hBMSCs). The results show that Mg doping can reduce the mesoporous order of MBG to a certain extent, but Mg-M/HT composite scaffold still has a uniform and ordered pore structure. Compared with M/HT scaffold, Mg-M/HT scaffold has higher intracellular focal adhesion proteins and integrins, as well as alkaline phosphatase, calcium nodules and osteocalcin expression, indicating that Mg doping can promote the osteoblast activity of M/HT scaffold. Mg-M/HT scaffold has a potential application in the field of bone tissue repair.