Reconstruction of large bone defects after bone tumor resection has always been a challenge. There are many reconstruction methods, such as tumor prosthesis, allograft, distraction osteogenesis, and autologous bone graft, each of which has its own advantages. In this report, we describe a new technique for the treatment of osteosarcoma by combining Ar-He knife cryoprobe with in situ replantation after resection of large segments of tumor bone. Methods: Osteosarcoma of the lower femur was surgically resected, and the tumor bone was frozen and inactivated by argon helium knife and then reimplanted in situ with internal fixation by plate screws. [RESULTS] There were no major intraoperative and short-term postoperative complications in the patients. At 3-month postoperative follow-up, the patient was able to walk off the crutches, and the active and passive range of motion of the knee joint was 0° to 40°. X-ray confirmed the formation of bone scabs at both ends of the replanted bone, but lung metastasis was observed. The X-ray showed significant resorption of the bone graft and loosening of the internal fixation at 15 months after surgery, but no tumor recurrence. Conclusion: The use of argon helium knife to freeze-inactivate long segments of osteosarcoma bone and then replant them in situ to achieve biological reconstruction is simple and effective. However, due to the small number of cases in this study and the short follow-up period, the long-term efficacy of this method needs to be further investigated.