The tendon pain behind the knee when walking can be caused by several reasons: first, osteoarthritis, severe osteoarthritis can involve the soft tissues behind the knee joint, which can cause the tendon pain behind the knee when walking, and this should be diagnosed by early examination, early x-ray and CT of the knee joint. Second, meniscal injury, when the posterior horn of the meniscus of the knee is damaged or torn, it can also cause pain in the tendons behind the knee when walking, especially when walking up and down stairs and squatting, which should be diagnosed by early examination of the MRI of the meniscus. Thirdly, popliteal bursitis, patients with popliteal bursitis can also experience pain in the tendons behind the knee when walking, which should be diagnosed and treated with an MRI of the knee joint.