The treatment of critical bone defects remains a significant challenge for advanced medicine. Chitosan/nano-hydroxyapatite (CS/nHA) composites have been widely developed in bone tissue engineering because of their attractive bioactivities. It has been demonstrated that incorporating a suitable amount of magnesium (Mg) into composite scaffolds can enhance the osteogenic effect. In this work, a series of bioactive porous composite scaffolds were prepared with polylactic acid (PLA), thermoplastic polyurethane (tPU), chitosan hydrochloride (CSH), nano-hydroxyapatite (nHA), and magnesium chloride (MgCl2) mixed by freeze-drying technology, namely, PLA/tPU-1Mg-CSH/nHA (PT-1M-CN), PLA/tPU-1.5Mg-CSH/nHA (PT-1.5M-CN), PLA/tPU-1.75Mg-CSH/nHA (PT-1.75M-CN), and PLA/tPU-2Mg-CSH/nHA (PT-2M-CN). Characterization analysis shows that the scaffold's surrounding structure is similar to cancellous bone, which may be suitable for bone defect filling. In vitro biological experiments indicated that all the scaffolds had good biocompatibility, promoting rat bone marrow mesenchymal stem cell (rBMSC) proliferation, migration and osteogenic differentiation. Furthermore, the in vivo studies suggested that the scaffolds played a specific "bridge" role in the interconnection of osteoblasts which enhanced bone regeneration. By contrast, all the findings showed that the PT-1.75M-CN scaffold had the strongest osteogenic ability. Therefore, because of the superiorities of rich raw materials, simple preparation methods, and easy mass production, the PT-1.75M-CN scaffold provides a promising strategy for developing and promoting bone regeneration and tissue engineering applications.