The causes of high fever in children aged 2.5 years include the following: First, it is caused by a severe lack of water in the child’s body. When oral antipyretic drugs are given to children with fever caused by infectious diseases, they are effective at first and the fever subsides after sweating, but after one or two days, the child’s body consumes too much water and parents do not pay attention to replenishment, which will cause the effectiveness of antipyretic drugs to decrease and cause the fever not to subside. In this case, it is necessary to give children timely fluid replacement, such as the application of oral rehydration salts. Second, it is caused by the lack of specificity of treatment. If the high fever in children is caused by the influenza virus, only the application of antiviral drugs such as oseltamivir or paramivir can have a good effect.