The pulmonary embolism mentioned in this article mainly refers to pulmonary thromboembolism, and how to prevent it, firstly, the mechanism of thrombus formation must be clarified in order to avoid risk factors. The thrombus of pulmonary embolism originates from the deep vein system, and the three main mechanisms of thrombosis shared by it mainly include: vein wall damage, hypercoagulable state and braking. First of all, the venous wall damage, if the deep vein is compared to a river, then the normal blood vessel is the smooth inner wall of the cement river, while the damaged blood vessel is the old and dilapidated inner wall of the stone exposed river, which mud and sand, i.e. thrombus is easy to deposit the result is self-evident. Clinically, trauma and surgery, especially of the lower extremities, such as femur fracture, femoral joint replacement surgery is the most common risk factor causing vascular endothelial injury, so once the fracture occurs in the elderly with osteoporosis, symptoms such as dyspnea and chest pain must be aware of whether pulmonary embolism occurs, and currently anticoagulation has been routinely used to prevent pulmonary embolism after orthopedic joint replacement surgery. The second is the high coagulation state, which is like the Yellow River water compared to the Li River water, the cement sand of the Yellow River with more coagulation material is easy to deposit, i.e. thrombus formation, so clinically those conditions can appear high coagulation? One is excessive blood cell density, that is, the blood is too thick, such as erythrocytosis (chronic hypoxic patients will compensate for the increase); another is increased pro-coagulation tissue, such as tumors, pregnancy (including 6-8 weeks postpartum), birth control pills and estrogen replacement therapy, smoking, surgery (vascular endothelial damage will activate coagulation) and congenital abnormalities of coagulation. Tumors are very important causative factors, among which hematologic, lung cancer, digestive system tumors and pulmonary embolism are the most relevant. Some patients with lung cancer start with pulmonary embolism and lower extremity deep vein thrombosis for the first time, and some unexplained pulmonary embolism may be followed for several years before the hidden hand turns out to be a tumor. Therefore, patients with tumors need to be alert to the corresponding symptoms of pulmonary embolism, especially chemotherapy drugs can lead to endothelial damage, and special attention needs to be paid to the presence of asymmetric edema in the lower limbs during chemotherapy. Patients with first-time pulmonary embolism need to be screened for tumors, and women also need to be screened for breast and gynecological systems. Once again, braking, bed rest and sedentary will lead to blood flow stagnation in the lower extremities, as if sediment is always deposited in the lower reaches of a slow-moving river. We often say: “life is movement”, movement will accelerate blood circulation, in addition to regular contraction of the lower limb muscle groups can constantly squeeze the deep veins to promote blood return. In life, long-distance travel, such as flying in economy class syndrome (ECS) refers to the syndrome of lower extremity deep vein and/or pulmonary embolism caused by flying, in addition to cars and trains can also increase the risk of lower extremity deep vein thromboembolism. There is also a risk of pulmonary embolism from leisure activities such as fishing and playing cards. The author once diagnosed a case of pulmonary embolism in an old man who was a fishing enthusiast. For example, we once diagnosed a case of puerperal pulmonary embolism, in which the patient was forced to “sit” in the moon for 4 weeks after delivery and did not get out of bed for half a month, which, together with poor appetite and high blood concentration and hypercoagulation due to heavy sweating, led to fever, chest pain, difficulty in breathing, and The patient was misdiagnosed as having pneumonia at one point. Therefore, patients at high risk, such as the elderly, oncology, maternity, and orthopedic surgery, avoid being sedentary and bedridden, and it is recommended to sit for one hour and then exercise appropriately, or if bedridden, perform lower extremity drive pump therapy in the hospital or exercise the lower extremities in bed. If there is asymmetric edema in the lower limbs, it indicates that thrombus has been formed, and then the patient should brake, not to mention physical therapy such as massage on the affected limbs, otherwise the thrombus can be dislodged and lead to pulmonary embolism once the lower limbs are moved. According to the cause, the prevention of pulmonary embolism is divided into three: primary prevention is the prevention of normal people, to prevent long time limb inactivity, and to pay attention to the movement of the lower limb every one hour by airplane or train; to prevent trauma, and massage should not be rough. Secondary prevention refers to the prevention of high-risk people, timely treatment of lower limb phlebitis and varicose veins; patients after surgery should get out of bed early to promote blood circulation, and drug anticoagulation prevention after orthopedic joint replacement. Tertiary prevention refers to the occurrence of pulmonary embolism, timely anticoagulation and even thrombolysis. Those with recurrent pulmonary embolism should be treated with long-term anticoagulation.