Deep vein thrombosis refers to thrombosis of the deep veins (s vein, femoral vein, inferior vena cava) in the lower extremities (abdominal cavity), which can occlude the deep veins and affect the blood flow back to the heart, resulting in swelling, pain, and sinking of the lower legs and/or thighs, as well as skin redness and fever if combined with inflammation. Due to the thrombosis, it can affect the function of venous valve, even after the thrombosis disappears, swelling of lower limbs in standing position still occurs, which is called venous valve insufficiency. The main danger of deep vein thrombosis is that the thrombus is dislodged and blocked along the blood flow or embedded in the pulmonary artery, leading to pulmonary hypertension and right heart failure, serious cardiogenic shock, and even sudden death. Deep vein thrombosis is mostly associated with bed rest (lower limb braking), surgery (trauma), such as hip surgery, pelvic fracture, cerebrovascular disease, chronic medical disease, etc., which may also be the result of easy embolism. The congenital causes are mainly due to hereditary deficiency of anticoagulant substances and increase of coagulant substances. The typical clinical condition of these patients is spontaneous or no obvious cause of lower extremity deep vein thrombosis or (and) pulmonary embolism, especially if it occurs before the age of 40. Acquired thrombophilia is most often seen in malignancies, antiphospholipid antibody syndrome, etc. The diagnosis of deep vein thrombosis is sometimes very difficult because not all patients with deep vein thrombosis present with lower extremity swelling, and sometimes the presence of lower extremity swelling is overlooked, especially in patients with surgery or trauma, and is often thought to be caused by surgery or infusion, but such thrombosis can still lead to fatal pulmonary embolism, so it is recommended that patients with major surgery or severe trauma should be routinely anticoagulated with heparin or low-molecular heparin anticoagulation in the perioperative period. For patients with lower extremity swelling, especially on one side with history of trauma (surgery) or pregnancy, or unexplained lower extremity swelling, such as unequal thickness and sensation of both lower extremities, deep vein thrombosis should be thought of and should be promptly investigated and hospitalized at a hospital in a position to do so. If not careful, once pulmonary embolism occurs, the mortality rate is very high, and the mortality rate can be as high as 35% for patients with severe pulmonary embolism who cannot be diagnosed and treated appropriately in time. In addition to perioperative anticoagulation, patients with a family history of thrombosis or malignant tumors should pay special attention to the possibility of thrombosis and be given anticoagulant drugs if necessary. For patients with long-term chronic diseases plus bed-ridden patients, attention should be paid to frequent active or passive limb movement, and anticoagulant drugs should be given when necessary to prevent deep vein thrombosis, such as patients with cerebral infarction hemiplegia. For people who work at a desk for a long time, sit in a car or an airplane for a long time, they should get up and move their limbs regularly. Although small doses of normal heparin are not effective for the prevention of reinfarction after myocardial infarction, they are effective for the prevention of deep vein thrombosis after acute myocardial infarction.