Fever is a symptom that can occur with many kinds of diseases, because the central nervous system is not well developed in children, and the regulation of body temperature by the thermoregulatory center is affected by many factors and is unstable, which often causes fever or the temperature to recede and then rise again. There are various causes of fever, which are summarized as follows: 1. Infectious causes: including early acute infectious diseases, various acute infectious diseases; 2. Non-infectious diseases such as neonatal dehydration fever, intracranial injury, etc.; 3. Metabolic reactions: such as allergies, inoculation reactions, infusion reactions, etc. If it is a long-term recurrent fever, sepsis, tuberculosis, rheumatic fever and various blood diseases, malignant diseases, etc. should be excluded. Various causes will be accompanied by corresponding symptoms, such as respiratory tract infections with coughing, coughing, breathing difficulties, etc.; gastrointestinal symptoms with nausea and vomiting, abdominal pain, diarrhea, etc.; central nervous disorders with convulsions, vomiting, coma, etc.; if it is a rash of various types, the pattern of appearance and distribution are also different. To clarify the cause, parents need to observe carefully and ask the pediatrician to make a diagnosis with the help of various related tests, not to make a blind judgment at home. If a child has a high fever accompanied by depression, apathy, drowsiness, restlessness, etc., it often indicates a serious condition and should be sent to a doctor as soon as possible without delay.