A bone defect is a partial loss of bone due to trauma, infection or tumor, or disease following the removal of a bone segment. Bone defects are relatively common in clinical practice. Loss of bone segments or bone masses in comminuted open fractures of the extremities; bone resorption from bone infection, removal of dead bone or removal of part of the bone after debridement are the most common causes. The traditional approach is to use autologous bone, homogeneous or allogeneic bone, and artificial bone grafting to resolve the problem. In infected defects this needs to be done after the infection has been controlled. Using an extension device of a bone external fixator, osteotomy at the normal site, application of bone lengthening at the osteotomy site, gradual sliding of the normal bone through the defect site, and finally re-establishing the continuity of the bone at the defect site is a method that has been used more often in recent clinical years. The bone segment sliding method does not need to destroy the normal part of the bone, and the bone comes from the autologous body without rejection and foreign body reaction. Especially in cases of infected defects, the defect can be treated while the infection is being treated, so there is no need to worry about the failure of bone grafting; it is also possible to carry out skin lengthening at the same time to solve soft tissue defects, which is the preferred method.