There are many causes of fever, including infection, metabolic abnormalities, autoimmune abnormalities, tumors, etc., which are not specific for the diagnosis of leukemia. Therefore, the diagnosis of leukemia cannot be made solely on the basis of the duration of fever, and requires a comprehensive analysis based on the patient’s other symptoms and test results. Leukemia symptoms do not only manifest as fever, but the main symptom is abnormal cell proliferation in the bone marrow. Due to the enhanced renewal of hematopoietic cells, impaired differentiation and blocked apoptosis in leukemia patients, their leukocytes are usually significantly elevated, with some patients having leukocytes above 50X10^9/L and even above 100X10^9/L. However, some leukemia patients can have significantly low leukocytes, which can lead to a decrease in the body’s ability to fight infection and various infections causing fever. The initial diagnosis of leukemia can usually be made if a patient presents with abnormal blood count combined with typical symptoms such as fever. In addition, patients with fever should keep warm and avoid getting cold to avoid aggravating the infection, and drink more water to replenish lost water, and if necessary, replenish water and electrolytes through infusion.