Abstract:[Objective] To study the design and surgical effect of 3D printed customized prosthesis of limb primary malignant bone tumor.[Methods] 14 patients of primary malignant long bone tumors treated with 3D printing customized prosthesis between June 2018 and December 2020, including 9 men, 5 women,9-57 years, average age of 18.5±13.8 years.The lesions were located in 9 cases of femur, 3 tibia and 2 humerus, all located in the sharft of the long bone. The pathological results were 10 cases of osteosarcoma, 2 cases of Ewing sarcoma, 2 cases of undifferentiated pleomorphic sarcoma. All?patients?were Enneking stage IIB. [Results] All 14 patients successfully completed limb preservation surgery. The follow-up period was 7-50 months with a mean duration of 23.7 ± 16.9 months.Two patients had postoperative complications, one patient with postoperative femoral osteosarcoma removed the hematoma, and one patient with postoperative radial nerve distraction, and recovered after 3 months of conservative treatment.The MSTS 93 system score 18-28, had an average score of 26.14±3.06. [Conclusion] Individualized 3D printed prosthesis can provide a choice for patients with malignant tumors located in the long bone shaft.