The causes of severe anemia may include aplastic anemia, hemolytic anemia and hemorrhagic anemia, and malignant blood system diseases. 1. Aplastic anemia: due to chemical, viral infection and immune factors, etc. damage to the hematopoietic system, so that the number of hematopoietic cells reduced or abnormal resulting in bone marrow hematopoietic failure, peripheral blood whole blood cell reduction. 2. Hemolytic anemia: due to the red blood cells themselves or other factors that cause red blood cells are easy to destroy, resulting in a reduction of blood cells in the body, and in severe cases, severe anemia can occur. 3. Hemorrhagic anemia: if serious trauma appears to be a large amount of blood outflow. In addition, malignant tumors may also cause nutritional disorders resulting in lack of hematopoietic substances, and severe anemia may also occur. 4. Malignant hematologic diseases: such as leukemia and myelodysplastic syndrome. There may be other causes of anemia of severe type, such as: tumor bone marrow infiltration, etc., you should go to the regular hospital in time, and the doctor will judge the cause of the disease according to the specific situation and give correct and timely treatment.