The common causes of pain on the back side of the knee are as follows: 1. Excessive dampness. Excessive dampness can cause pain in the back of the knee and the patient’s knee joint will feel sore. 2. Soft tissue contusion of the knee joint. Soft tissue of the knee joint mainly refers to the skin, muscles, ligaments, nerves and other tissue parts of the knee joint. If these tissues are abnormal due to external forces, the patient’s knee joint area will have obvious symptoms of pain, muscle spasm, dysfunction, and even ligamentous laxity.3. Excessive weight, because the knee joint is one of the most important weight-bearing parts of the body, being overweight will lead to abnormal pressure on the knee joint for a long time, resulting in muscle pain in the back of the knee joint.4. Excessive exercise, excessive exercise and strenuous exercise in daily life The painful phenomenon of the tendons in the back of the knee joint is easily caused by excessive exercise, which can easily damage the knee joint, thus bringing pain to the knee joint and even causing ligament damage to the knee joint.