According to the normal range of white blood cells, 20×10⁹/L of white blood cells for fever is a high value and is considered severe. The normal range of leukocytes varies from one population to another, with adult leukocytes generally in the range of (4.0~10.0)×10⁹/L. Whether or not it is severe depends on the specific cause of the illness, such as infections and hematologic disorders. 1. White blood cells are an indicator of inflammation and infection. If white blood cells are elevated, it means that there may be an infection present. However, some physiological reasons cannot be ruled out, such as strenuous exercise or physical labor, excessive emotional tension, etc. can cause physiological white blood cells to rise. Fever is usually a sign of infection. If the fever is accompanied by elevated white blood cells, it may be related to bacterial infection. Anti-infection treatment is needed, including levofloxacin. 2. Fever with elevated white blood cells cannot be ruled out as a manifestation of blood diseases, including acute leukemia and myelodysplastic syndrome. At this time is more serious, need to be targeted treatment, such as acute myeloid leukemia to be a sugar cytosine, Zoerythromycin and other drugs. Therefore, when the fever and accompanied by elevated white blood cells, we should go to the hospital in a timely manner, improve the relevant examination, clear cause of the disease in the physician’s guidance to carry out targeted treatment.