1. Infections: (1). Certain viral infections, which are common causes of granulocytopenia in the infection category, such as influenza, viral hepatitis, infectious mononucleosis, etc. (2). Certain gram-negative bacterial infections, such as typhoid fever, paratyphoid fever, etc. (3). Certain protozoal infections: such as malaria, black fever, etc. 2. Hematologic diseases: such as aplastic anemia, megaloblastic anemia, hypoproliferative leukemia, myelodysplastic syndrome, metastatic cancer of bone marrow, etc. Physical and chemical damage: (1) drugs: such as anti-tumor and immunosuppressive drugs, anti-diabetic drugs, antibiotics, etc. (2) Chemical substances: such as benzene, lead, mercury and other poisoning . (3) Radiation damage, radioactive substances can directly damage hematopoietic stem cells and bone marrow microenvironment. 4. Monocyte-macrophage system hyperfunction: such as hypersplenism, portal cirrhosis and other diseases. 5. Increased immune destruction: such as neonatal alloimmunization, autoimmune liver disease.