Fever dehydration is mainly a result of massive water loss in the body, as well as loss of salts in the body, which in turn leads to a severe reduction in extracellular fluid. Fever dehydration is caused by dehydration due to increased body temperature, but also due to the loss of excessive water in the body when taking antipyretics and sweating heavily. Symptoms such as thirst, dry skin and mucous membranes, loose skin with poor elasticity, little or no urine, high fever, and lack of sweating usually occur. If dehydration is severe, it can lead to hoarseness and rapid heart rate due to insufficient effective blood volume. If dehydration can not be corrected in time, it will allow the loss of intracellular fluid, the appearance of thirst symptoms to reduce the “illusion”, severe dehydration can lead to mania, hallucinations, and even coma, shock and acute renal failure and other serious consequences. It is recommended that when a fever causes dehydration, the patient needs to be rehydrated, and it is best to supplement with light sugar saline or oral rehydration salts. It is recommended to seek prompt medical attention and actively search for the cause of fever, as well as replenish lost body fluids, as well as cooling treatment.