The 20-day-old baby belongs to the newborn, and fever must be given high priority because newborns rarely have fever, once fever usually indicates that the infection is very serious, prone to sepsis, sepsis, and even central nervous system infection or pneumonia. If the fever is high, newborns because the thermoregulatory center is not perfect, you can open the clothes properly, wear looser clothes, should be able to reduce the fever, if still can not reduce the fever, you can take physical cooling, such as paste cooling paste or give the baby a warm bath, etc., can assist in reducing fever. After the fever has gone down, you should take your baby to the hospital as soon as possible and consult the pediatric emergency department or neonatal clinic for further tests, such as blood tests, C-reactive protein, calcitoninogen and other tests to understand the status of the infection, which may require hospitalization for observation or inpatient treatment.