Knee pain down the stairs may have the following causes: first, injury to the meniscus, when the meniscus posterior horn has damage or tear, it can appear down the body flexion joint when the joint obvious pain, to carry out MRI examination of the knee joint, to carry out early diagnosis and treatment. Second, patellofemoral arthritis, young people due to long-term body movement, or due to long-term long-distance walking, resulting in inflammation of the patellofemoral joint, cartilage damage, can appear down the stairs when the patella or cartilage friction, resulting in pain, to carry out X-ray, CT examination of the knee joint, to diagnose and treatment. Third, osteoarthritis, when the knee joint has severe osteoarthritis, it can involve the patellofemoral joint and meniscus, which can lead to obvious pain in the knee joint when going down the stairs, and early X-ray and MRI of the knee joint should be performed for diagnosis and treatment.