Pain in the hamstring behind the knee may be caused by peripheral tendon injury, osteoarthritis and lumbar disc herniation. 1. Peripheral tendon injury: it may be due to the patient’s long-term lower limb exercise, which leads to strain on the tendons, ligaments and other soft tissues around the knee joint, stimulating the nerve tissue, thus causing pain. 2. Osteoarthritis: it may also be caused by patients suffering from arthritis or rheumatoid arthritis, etc. Due to the stimulation of inflammation and damage to cartilage tissues, the friction between bones and joints can not be effectively cushioned and load-bearing, and then there will be pain in the hamstring behind the knee. 3. Lumbar disc herniation: pain in the sciatic nerve area behind the knee caused by a herniated lumbar disc that compresses the nucleus pulposus and nerve roots. Therefore, it is recommended that the patient go to the hospital for consultation, after clarifying the cause of the disease, under the guidance of professional doctors, targeted treatment.