Leukemia is a common malignant tumor of the blood system that poses a great threat to human health, and the cause of leukemia is still not very clear. The precursors of leukemia are: first, the precursors of anemia, some patients with leukemia may have mild pallor, dizziness and weakness, and feel a loss of strength and limb weakness after activity. Second, the precursor of infection, some leukemia patients may appear mild fever, manifested as a low fever, which lasts for a long time, most people mistaken for a cold, taking cold flush treatment is not effective, with the progress of the disease may gradually appear high fever. Third, the precursors of bleeding, some patients may appear skin mucous membrane bleeding spots, petechiae, however, there is often no obvious nasal, gum bleeding and other conditions. IV. Precursors of superficial lymph node enlargement. Some patients may have swollen lymph nodes in the neck, supraclavicular area, etc., but no painful sensation.