The danger period of pulmonary embolism is related to the criticality of the patient’s condition and cannot be generalized. Patients with massive pulmonary embolism have severely impaired hemodynamics and are in danger at any time. Shock and impaired consciousness can occur at any time, so timely thrombolysis and anticoagulation are needed to save patients’ lives and reduce the rate of death. However, after the embolism is lifted, the patient is basically hemodynamically stable, but close observation is also required within 7-10 days, during which the patient is still at risk and secondary embolism may occur. For patients with non-massive embolism, with mild clinical symptoms and relatively stable hemodynamics, anticoagulation can be performed without thrombolysis, but they should also be closely observed for 7-10 days to avoid further aggravation of embolism. In addition, patients with pulmonary embolism typically present with chest pain, hemoptysis, and dyspnea. If all three symptoms occur at the same time, the first consideration should be pulmonary embolism, and CT angiography should be performed immediately for immediate treatment upon diagnosis.