A child’s persistent fever of 39 degrees is dangerous and may lead to febrile convulsions, cerebral edema and respiratory failure. As the child’s nervous system is not well developed, the child’s persistent fever of 39 degrees may cause central nervous system dysfunction, fever convulsions, repeated fever convulsions may cause brain cell damage, and even affect the child’s normal intelligence. Persistent fever of 39 degrees may also lead to hypoxia, mild hypoxia can appear restlessness, drowsiness and other symptoms, severe hypoxia can cause cerebral edema, convulsions, coma and other serious consequences. Children with persistent fever of 39 degrees can also cause some degree of harm to the heart. The child may have a rapid heart rate, respiratory arrhythmia and other symptoms, caused by fever associated with viruses, bacteria may be secondary toxic myocarditis, severe cases will also lead to death due to heart failure. Therefore, if a child has a persistent fever of 39 degrees, parents should pay attention to it, give appropriate antipyretic, and bring the child to the doctor in time to clarify the cause of the fever, and then carry out the treatment of the cause.