Fever is an increase in body temperature due to various causes and is one of the common accompanying symptoms. Patients who often have prolonged fever for which no cause can be found are often seen in clinical practice. Fever can be caused by a variety of diseases, seen in infectious and non-infectious diseases. Infectious fever currently has 9 major pathogens, and different pathogens are treated with different drugs; non-infectious fever is divided into malignant tumors, immune system diseases, drug fever, etc. It may also be due to dysfunction of the thermoregulatory center, such as heat stroke, cerebral hemorrhage, encephalitis and brain tumors, etc. If fever does not subside, the reason may be incorrect diagnosis, or incorrect treatment medication, or insufficient treatment time. Therefore, in addition to physical cooling and medication to reduce fever, finding the cause of the fever and treating the cause is the main measure to treat fever. This requires patients and their families to visit the infectious disease department of the hospital and cooperate with the doctor to do relevant tests and auxiliary examinations to clarify the cause as early as possible in order to completely eradicate the cause of the fever. However, if the body temperature exceeds 40℃ (more than 39℃ in children) it may cause convulsions, coma, or even serious sequelae, and comprehensive antipyretic measures should be taken promptly to cool down rapidly to prevent high fever convulsions, heat stroke, and brain cell damage.