The general theory is that damage to the vessel wall, abnormal blood flow and altered blood composition are the 3 main factors that cause venous thrombosis. The change of blood composition into a hypercoagulable state is the determining factor of DVT formation. 15 susceptibility factors: 1, age: age increases, the incidence rate gradually increases, the incidence rate of 80-year-old people is more than 30 times that of 30-year-old people. 2, braking: clinically it is often seen that patients who are bedridden for a long time are prone to DVT, and the venous blood return is significantly slowed down after braking, which increases the risk of DVT development. 3, history of venous thrombosis 23% to 26% of patients with acute DVT have a previous history of venous thrombosis, and these newly formed thrombi are often from the original lesion of the vein. It was found that the blood of recurrent DVT patients is often in a hypercoagulable state. 4, malignant tumors Statistics found that 19% to 30% of DVT patients combined with malignant tumors, lung cancer is the most likely to cause DVT of a malignant tumor, other malignant tumors such as genitourinary system and gastrointestinal system is also prone to complicate DVT. 5, surgery: surgery is an important susceptibility factor of DVT, the type of surgery is particularly important. The incidence of DVT after general surgery is about 19%, neurosurgery is about 24%, while femur fracture, hip arthroplasty and knee arthroplasty are as high as 48%, 51% and 61% respectively. 6, trauma: autopsy of traumatic death found that 62% to 65% of the deceased had DVT occurrence. 7, primary blood hypercoagulable state: common in patients with genetic mutations or hereditary anticoagulant defects, 5% to 10% of all DVT patients are caused by primary blood hypercoagulation. 8.Postpartum:The incidence of postpartum DVT is high, while DVT patients during pregnancy in China is less common. 9, oral contraceptives: oral contraceptives are prone to DVT, it has been found that 1/4 of women of childbearing age suffering from DVT are related to taking contraceptives, and the DVT complication of women of childbearing age taking third-generation contraceptives is 8 times of those not using contraceptives. 10, blood type: it has been found that blood type has a certain relationship with DVT, people with A blood type are most likely to suffer from DVT, relatively speaking, O blood type has the least risk of DVT. 11.Ethnicity: The incidence of DVT is much higher in Europe than in Asia, and the difference of living habits and dietary structure may also affect the occurrence of DVT. 12, central venous cannulation: clinically, central venous cannulation is increasing, making the incidence of DVT also increased accordingly, especially in the upper extremity DVT patients 65% of the patients with central venous cannulation related. 13, enterocolitis Pulmonary embolism in patients with enterocolitis is often reported clinically. 14, systemic lupus erythematosus systemic lupus erythematosus patients are often combined with arteriovenous thrombosis, 15, other: obesity, varicose veins of the lower extremities and cardiac insufficiency are still debated whether they are susceptibility factors of DVT, multi-factor statistical analysis that obesity, varicose veins of the lower extremities and cardiac insufficiency are not independent susceptibility factors.