If the leg suddenly swells up, the first reason to consider is lower limb vein thrombosis, which can be improved by lower limb vein ultrasound examination to clarify the diagnosis. Lower limb vein thrombosis is mainly related to the patient’s reduced activity, such as after major surgery, long-term bed rest, and impaired limb movement due to cerebrovascular disease. High age, low water consumption, malignant tumor, position during surgery, emergency, etc., which put the blood in a hypercoagulable state, also play a role in the occurrence and development of the disease. In addition, the causes of leg swelling are also related to diseases such as hypoproteinemia, renal insufficiency and cardiac insufficiency, which require further examination to clarify.