There are many reasons for the formation of blood clots in the legs, mainly in the following three aspects: I. Damage to the blood vessel wall, such as surgical damage to blood vessels or local venous puncture, can cause thrombosis. Second, hypercoagulable state, such as advanced tumor, severe dehydration, anesthesia recovery patients, and long-term bedridden patients are caused by patients with hypercoagulable state, after hypercoagulable state of blood coagulation, then the formation of blood clots in the legs. Third, blood coagulation factor abnormalities, such as hemophilia or congenital coagulation dysfunction, or thrombocytosis hypercoagulable state are high-risk factors leading to thrombosis. The biggest risk after the formation of leg thrombosis is thrombus dislodgement to form fatal pulmonary embolism, so the leg thrombosis must pay attention to avoid thrombosis.