Computed tomography is used in 13 clinic cases with bone malignant tumor to get 2-dimensional data of diseased area. Reconstruction of 3- dimensional anatomical model, excision range of bone, designing of individual surgical template and bone prosthesis was accomplished preoperatively by computers. Based on computer-assisted-design (CAD) proposal, we cut the tumor accurately, and use allografts bone with personalized prosthesis to reconstruct the bone defect after tumor excision. It is concluded that we can design excision range of bone easily, cut them accurately, reconstruct bone defect of diseased area precisely with the CAD technology.