There are about three ways to classify anemia: first, according to the cell dosimetry classification, it is divided into macrocytic anemia, normocytic anemia, and small cell hypochromic anemia. Large cell anemia has an average red blood cell volume >100fl and hemoglobin >32g/L, normocytic anemia has an average red blood cell volume between 80-100fl and red blood cell hemoglobin content of 26-32g/L, and small cell hypochromic anemia has an average red blood cell volume <80fl and red blood cell hemoglobin <26g/L. Second, according to the severity, it is classified into mild, moderate, severe and very Severe anemia, mild anemia with hemoglobin >90g/L but below normal value. Moderate anemia with hemoglobin between 60-89g/L. Severe anemia with hemoglobin between 30-59g/L. Very severe anemia, hemoglobin <30g/L. Third, according to the etiology and pathogenesis, there are erythropoiesis-decreasing anemia, erythrocyte destruction-increasing anemia, i.e. hemolytic anemia, and blood loss.