Lower extremity thrombosis generally refers to deep vein thrombosis in the lower extremity. A typical lower extremity DVT is when a vein is completely blocked by a venous thrombosis, often with an acute onset, such as a significant swelling of the lower extremity that was normal last night when one wakes up in the morning. The pathological changes are caused by the obstruction of blood flow back to the legs, and as the blood stagnates in the legs, the patient’s legs become edematous and swollen, with superficial venous dilatation and increased local skin temperature. Severe hood venous stasis and swelling will compress the arterial blood supply to the lower limb, which can cause ischemia of the limb, and the limb will appear cold, pale, numb and other manifestations of insufficient arterial blood supply, i.e. femoral cyanosis or femoral leukodystrophy, which should be actively operated to improve the arterial blood supply. Otherwise, it will lead to limb necrosis or even have to do amputation surgery. When the lumen is not completely blocked by deep vein thrombosis in the lower extremity, it often does not cause obvious discomfort of swelling of the limb, or even any uncomfortable any symptoms. For example, like deep vein subvalvular thrombosis. Both completely occluded thrombi in the deep veins and partial thrombi can lead to pulmonary artery embolism when dislodged. About 1/3 of pulmonary artery thromboses have no obvious clinical symptoms, and 1/3 will present with discomfort such as chest pain, dyspnea, or may even be the only symptomatic manifestation of lower extremity DVT. Another about 1/3 are pulmonary artery trunk embolism, and sudden death often occurs. Besides judging the leg thrombosis from symptomatic manifestations, further examinations such as ultrasonography, arteriography, and lower extremity venous cascade angiography are needed to clarify the cause and lesion site and to formulate a treatment plan.