Lower limb swelling is very common, some are caused by heart, liver and kidney diseases, some are caused by lower limb vein diseases, among which deep vein thrombosis is the most urgent condition. 1.Incidence rate The incidence rate of deep vein thrombosis: foreign data is 1.6%, triggering pulmonary embolism: 20~50%, death: 150~200,000 in the United States every year. 2.Clinical manifestations: swelling of limbs, pain in limbs, increase of skin temperature, pressure pain along veins, dilated or varicose veins. 3.Harm ①Pulmonary embolism. Chest pain, dyspnea, cyanosis, coma, hemoptysis, sudden death. ②Sequelae of venous thrombosis. Varicose veins, swollen and painful limbs, eczema of skin, ulcers of lower limbs. 4.Risk factors Advanced age, hypercoagulable state of blood, malignancy, postpartum, prolonged bed rest, long distance travel, surgery (especially pelvic and orthopedic surgery), trauma, oral contraceptives, heredity, infection, inflammation, smoking, chronic bronchitis. 5. Diagnosis and treatment Diagnosis Color ultrasound, phlebography, blood tests. Treatment Medication, surgery (one week embolization to protect the function of venous valves is effective), minimally invasive treatment. 6.Prevention Drug prevention, wearing medical elastic stockings, appropriate walking exercise.