When the bone defect surpasses the critical threshold for self-repair, an interventional bone scaffold is required to restore structural integrity and function. Load-bearing bones scaffold need to have sufficient mechanical strength and appropriate porosity. Topology optimization as a potential design method can meet the above requirements. In this study, a topology optimization approach with smooth boundary based on grid point density was proposed to optimize the load-bearing bone scaffold. The applicability of the established method was demonstrated by designing bone scaffold structures with different porosities. In addition, the mass transfer characteristics of the bone scaffold were verified by fluid simulation. The method established in this paper provides a reference for the design of load-bearing bone scaffolds.