Syncope is a sudden loss of consciousness in a patient, and the symptoms may disappear completely after rest. Syncope is not a separate disease, but often a syndrome caused by multiple etiologies. The main causes of syncope are the following.1. Cardiogenic syncope needs to be considered: such as arrhythmia,, dirty valve disease, myocardial infarction, etc.2. Cerebral syncope: such as severe cerebral artery occlusion or stenosis, hypertensive encephalopathy, etc.3. Reflex syncope: such as syncope induced by urination, swallowing, violent coughing, etc.4. Other causes of syncope need to be considered, such as crying syncope, syncope caused by hypoglycemia, or syncope induced by severe anemia. Patients need to go to the hospital promptly after sudden syncope to improve the examination, identify the cause and treat the symptoms.