1.Decreased hematopoietic function: the bone marrow hematopoietic function gradually decreases with age; 2.Nutritional factors: reduced intake of hematopoietic raw materials such as iron, folic acid and vitamin B12 due to partial diet or reduced dietary intake; 3.Secondary anemia: anemia caused by other diseases, common causes include: malignant tumor, liver disease, chronic renal insufficiency, chronic infection, endocrine abnormalities 4.Environmental factors: damage to hematopoietic function due to environmental pollution and exposure to harmful substances.