Objective To investigate the related factors affecting the degree of anemia of preterm infants. Methods The clinical data of 167 preterm infants within 24 hours after birth admitted to the department of neonatology in Zhuhai Women and Children's Hospital from June 2012 to June 2013 were collected.The preterm infants were classified into two groupsmild to moderate anemia group and severe anemia group.All clinical data were analyzed by single factor analysis and Logistic regression. Results The birth weight,gestational age of the severe anemia group were significantly lower than the mild to moderate anemia group,the difference was statistically significant (P<0.01).The length of hospital stay,iatrogenic blood loss were obviously higher than the mild to moderate anemia group,the difference was statistically significant (P<0.01).The birth weight and the length of hospital stay were risk factors of severe anemia. Conclusions The degree of anemia is associated with the birth weight,gestation age,length of hospital stay and iatrogenic blood loss.The birth weight and the length of hospital stay are independent risk factors of severe anemia in preterm infants.