Fever during the day without fever at night may be caused by autonomic dysfunction, infection, vagal excitation affecting the metabolism of heat, and so on. 1. Infection, pathogenic microbial infection will cause inflammatory cells to release inflammatory mediators, which will cause the thermoregulatory center to become impaired and the hypothalamic thermoregulatory point to fluctuate. During the daytime due to a variety of activities to the body’s ability to resist these inflammatory mediators is slightly higher, while at night the body’s activities are weakened, its ability to resist these inflammatory mediators is reduced, the daytime body temperature may be normal and the night body temperature high symptoms. 2. Autonomic dysfunction, mostly caused by social factors, such as long-term stress, anxiety, etc., and reduced activity at night and no contact with the outside world. In a quieter situation, the spirit is easy to be highly concentrated, the chance of anxiety, nervousness and other symptoms is large, so it may lead to a higher body temperature at night. 3. Vagus nerve excitation affects heat metabolism, the human body is in a quiet state at night, the vagus nerve is excited during sleep, the body temperature is slightly shifted upward, resulting in a higher body temperature at night than during the day. And the hormone secretion level is different between daytime and nighttime, there will also be a difference between daytime and nighttime body temperature. Daytime fever at night may also be due to other reasons, should be as soon as possible to the local regular hospitals, accept the guidance of the doctor’s treatment, do not delay, so as not to delay the condition.