High erythrocyte count in fever is considered to be due to the fact that after fever, the patient discharges body fluids out of the body by means of insensible evaporation, etc., which plays a role in cooling down the body. With the discharge of body fluids, the body fluids will gradually concentrate, and the red blood cell values in the blood will be high. When the fever is high, the cause of the fever should be clarified in the hospital and the corresponding symptomatic medication should be given, and antipyretic and analgesic medication can be taken orally when the body temperature exceeds 38°C. With the effective treatment of medication, the body’s laboratory indicators will return to normal. In addition, a few patients may have elevated red blood cells accompanied by fever due to blood system diseases.