The red blood cell volume distribution width (RDW) is obtained by measurement with a hematocrit analyzer and is a parameter that reflects the heterogeneity of the peripheral blood red blood cell volume. What it expresses is the degree of homogeneity of red blood cell volume size. If the red blood cell volume size is homogeneous and consistent, the parameter is lower and within the reference range. If the erythrocyte volume size is inconsistent and varies widely, the parameter is higher than the reference value. The morphological characteristics of erythrocytes are different in anemia caused by different etiologies. RDW can be used for early diagnosis and efficacy observation of iron deficiency anemia; RDW/MCV combination is also used for morphological classification of anemia, etc. The prevention of red blood cell volume distribution width needs to pay attention to several aspects: strengthen education on nutrition and correct partial eating habits and incorrect cooking habits. Infants should be promoted to be breastfed and fed rationally. In areas with high prevalence of nutritional megaloblastic anemia recipes should be actively promoted for improvement. Folic acid prophylaxis should be given to those with chronic hemolytic anemia or long-term antiepileptic drugs, and total gastrectomy patients should be given prophylactic intramuscular injection of vitamin B12 once a month. Strengthen education on nutrition and correct partial eating and poor cooking habits. Do not abuse alcohol. Patients on hemodialysis and gastrointestinal surgery should strengthen nutrition and supplement folic acid and vitamin B12. folic acid and vitamin B12 should be supplemented in time when taking drugs that affect the absorption and utilization of folic acid and vitamin B12. infants should advocate breastfeeding, reasonable feeding and timely addition of complementary foods. Pregnant women should eat more fresh vegetables and animal protein, and supplement folic acid in the second trimester.