Pulmonary embolism is a pathological change in which the pulmonary artery and its branches are obstructed by emboli, interrupting the blood flow to the corresponding blood supplying lung tissue and causing necrosis of the lung tissue. Elderly people are bedridden for a long time, bedridden after surgery, postpartum and after trauma are prone to form venous thrombosis and embolism. The disease is a critical condition, and sudden death can often occur. The disease is not rare, and is easily misdiagnosed or missed clinically, and is often confirmed from autopsy. The clinical manifestations of pulmonary embolism are diverse and actually represent a broader clinical spectrum. It is mainly determined by the number of blocked blood vessels, the speed of occurrence and the underlying state of heart and lungs. In mild cases, 2 to 3 lung segments can be asymptomatic; in severe cases, 15 to 16 lung segments can lead to shock or sudden death. The main manifestations of pulmonary embolism are: 1.Acute pulmonary heart disease Sudden dyspnea, near death feeling, cyanosis, right heart failure, hypotension, wet and cold extremities, seen in patients with sudden embolization of more than two lung lobes. 2.Pulmonary infarction Sudden dyspnea, chest pain, hemoptysis and pleural friction sounds or pleural effusion. 3.”Unexplained dyspnea” The relatively small embolic area is the only symptom suggesting an increase in ineffective cavity. 4, chronic recurrent pulmonary thromboembolism Slow onset, late detection, mainly manifesting as severe pulmonary hypertension and right heart insufficiency, is a type of clinical progression. There are also rare paradoxical embolism and non-thrombotic pulmonary embolism. The former is mostly a stroke coexisting with pulmonary embolism, caused by the opening of the oval foramen in pulmonary hypertension and the venous emboli reaching the body circulatory system; the latter may be a fat embolism syndrome caused by long bone fracture or an air embolism associated with a central venous catheter.