There are two main causes of fever in leukemia: 1, leukemia itself can cause fever, leukemia cells themselves are abnormal cells, abnormal cells appear in the blood can be used as a source of fever; 2, leukemia patients have a very low immune status, which can lead to infectious fevers, is the problem caused by pathogenic bacteria, a variety of factors can cause infection. Common viral, bacterial, fungal infections, medically known as called opportunistic bacteria, the incidence of their infections are higher. In clinical practice, the cause of the disease is differentiated. If the disease itself is the cause, the disease is treated. If the infection factor is considered to be the cause, this time, on the contrary, we should suspend the treatment of the original disease, if already infected and then chemotherapy, is equivalent to give the patient a more significant blow, the infection will be aggravated, and even life-threatening. Therefore, chemotherapy should be put on hold at this time, and antipathogenic bacteria treatment should be carried out first.