Swelling at the ankle can be caused by the following reasons: First, lower limb vascular diseases: varicose veins or phlebitis of lower limb veins, venous valve insufficiency, etc. can lead to lower limb venous reflux obstruction and swelling at the ankle, which should be diagnosed by checking the ultrasound of lower limb blood vessels. Second, immune system diseases: rheumatism and rheumatoid diseases can also involve the ankle joint and cause swelling and pain in the ankle. Thirdly, large osteoarthrosis: Patients with large osteoarthrosis can have clinical manifestations such as swelling, deformity and pain of the ankle. Fourth, old injury: If the ankle is sprained, it can lead to swelling and pain in the ankle, and the diagnosis and treatment should be made according to the patient’s medical history and the X-ray of the ankle.