There are many causes of knee pain, such as osteoarthritis, rheumatoid arthritis, tuberculous arthritis, meniscus injury, bone fracture and synovitis caused by trauma, etc. This kind of pain will improve after rest and treatment. If there is no obvious cause for the pain, and the pain worsens progressively, does not get better after resting, and does not improve with regular treatment, then it is necessary to be alert to the possibility of cancer pain. Cancer of the knee joint is relatively rare, and the most common are primary malignant bone tumors, such as osteosarcoma, Ewing’s sarcoma, and giant cell tumor of bone, etc. Usually, bone metastatic cancers occurring around the knee joint are less common. Most of the cancerous painful knee joints develop unilaterally, often with swelling and lumps in the knee joint. If the patient has these symptoms, it is recommended to go to regular tertiary hospitals for a specialized and comprehensive examination, such as X-ray, CT and nuclear magnetic resonance (NMR) of the knee joint, in order to exclude the possibility of cancerous painful knee joints.