Osteosarcoma is one of the most common primary malignant bone tumors. Although the incidence of malignant bone tumor, commonly known as “bone cancer”, is not high, it is highly malignant and has a high death and disability rate, and it mostly occurs in children around 10 years old. Like other malignant tumors, early detection, early diagnosis and early treatment (i.e. “three early”) are the keys to successful treatment of malignant bone tumors, especially with the introduction and promotion of neoadjuvant chemotherapy in the last 20 years, the treatment effect of such diseases has been significantly improved. However, due to the lack of specific symptoms in the early stage of malignant bone tumor, it is often not easy to attract the attention of children and parents when it develops, or it is considered as growing pain or common trauma, so many children are diagnosed late and lose the opportunity of early treatment, and the prognosis is poor. Malignant bone tumors are mostly found in long tubular bones such as femur, tibia and humerus, with distal femur and proximal tibia, i.e. around knee joint, being the most common. With the progress of the disease, the pain is progressively aggravated, the pain site is fixed, local swelling can gradually appear, the skin temperature is higher than the opposite side, some children may be accompanied by fever, poor appetite, anemia and other symptoms. If these symptoms appear, it indicates that the disease is already progressing rapidly and it is time to consult a doctor as soon as possible for a clear diagnosis. Therefore, parents are reminded that if your child has unexplained pain around the joint or if the pain cannot be relieved after resting for more than 1 week after minor injury, they should be alert to the possibility of malignant bone tumor and should take the child to a specialized hospital for consultation in time. We also remind non-bone tumor doctors to be extra cautious when seeing such children. For children with no obvious abnormality in general X-ray, they should be advised to follow up or have MRI examination if necessary, and not to delay the diagnosis and treatment because of growing pain or soft tissue injury.