Neoadjuvant chemotherapy refers to chemotherapy before surgery, surgery after chemotherapy, and chemotherapy after surgery. Among them, the significance of preoperative neoadjuvant chemotherapy includes three aspects: 1. to kill the possible micro metastases, including those in the blood; 2. to make the tumor shrink and the boundary clear, so as to create conditions for surgery, increase the limb preservation rate of osteosarcoma and reduce the recurrence rate of osteosarcoma; 3. to judge the effect of chemotherapy, so as to facilitate the formulation of chemotherapy plan after surgery. When the tumor necrosis rate is >90%, it proves that the preoperative chemotherapy program is effective and can be continued after surgery; when the tumor necrosis rate is <70%, it indicates that the postoperative chemotherapy may need to adjust the program.