Patients with deep vein thrombosis often ask, “Why did I get deep vein thrombosis? There are many causes of DVT, often multiple causes exist at the same time. There are three main factors: 1. Blood flow stagnation The blood flow stagnation here does not refer to the “blood stagnation” in Chinese medicine, but is like a river that has lost its vitality, the flow rate changes, or even stops flowing. This is the most common factor. This is especially true in patients with cerebrovascular disease, heart disease, post-surgery, malignant tumors, and other long-term bed rest and orthopedic diseases with lower limb braking. The mechanism may be related to continuous supine position, continuous compression of the posterior iliac veins of the pelvis by the pelvic organs and reduced muscle movement of the lower limbs. Blood flow stasis can occur in disease states as well as in healthy populations. Pregnancy is a classic example. Increased blood in the uterus and ovaries in pregnancy increases blood flow in the pelvic veins, and the enlarged uterus compresses the lower extremity veins, blocking venous return. And obesity, long airplane ride, keeping the same body position and little activity of lower limb muscles will affect the lower limb venous blood return. 2.Venous wall abnormality Due to trauma, intrapelvic surgery, femoral neck surgery, various catheterization, intravenous catheter retention, high tension fluid injection caused by venous wall damage, endothelial stripping, thus causing platelet attachment, coagulation factor activity changes, may form thrombus. In actual clinical work, deep vein thrombosis without the above factors is not uncommon. 3, hypercoagulation Dehydration, shock, erythrocytosis, etc. lead to blood concentration and increased blood viscosity, trauma, surgery, large release of prothrombin, malignant tumors, frequent oral contraceptives, pregnancy, prostate cancer, etc. are likely to produce thrombosis. Those with congenital abnormalities of coagulation inhibitory factors are more prone to deep vein thrombosis, and AT-III deficiency, protein C deficiency, and protein S deficiency, which show familial onset and recurrent occurrence, combined with a high incidence of refractory pulmonary embolism, suggest the involvement of genetic factors.