BackgroundLimb salvage surgery is the preferred treatment for most malignant bone tumors, but postoperative infection treatment is very challenging. Simultaneously controlling infection and solving bone defects are clinical treatment challenges.Case PresentationHere we describe a new technique for treating bone defect infection after bone tumor surgery. An 8‐year‐old patient suffered an incision infection after osteosarcoma resection and bone defect reconstruction. In response, we designed her a personalized, anatomically matched, antibiotic‐loaded, bone cement spacer mold using 3D printing technology. The patient's infection was cured, and limb salvage was successful. In follow‐up, the patient had returned to normal postoperative chemotherapy and was able to walk with the help of a cane. There was no obvious pain in the knee joint. At 3 months after operation, the range of motion of the knee joint was 0°–60°.ConclusionThe 3D printing spacer mold is an effective solution for treating the infection with large bone defect.