The main causes of blood clots in the legs include damage to the vessel wall, high blood viscosity or hypercoagulable state, abnormal clotting factors, and hemodynamic abnormalities. 1. Vascular wall injury: trauma, surgery or local venous puncture and other causes of vascular wall injury, can cause local hematoma, thrombosis. 2. High blood viscosity or hypercoagulable state: such as hyperlipidemia, thrombocytosis, advanced tumor, severe dehydration, anesthesia recovery period, etc., are prone to thrombus formation. 3. Abnormal coagulation factors: such as hypercoagulable state of blood, congenital coagulation dysfunction, etc., which are high-risk factors for thrombosis. 4. Abnormal hemodynamics: stenosis of blood vessels, varicose blood vessels, prolonged squatting and standing, prolonged bed rest, cold and dampness, etc., which can lead to poor blood flow, increased intravascular pressure, and endothelial damage, triggering the formation of thrombus. If you have any discomfort in your legs, you need to check and diagnose in time, and do angiography if necessary. After the formation of thrombus, do not do strong exercise, do not press to prevent dislodgement, pay attention to warmth, timely medical care.