Meeting the Inclusion Criteria of this study will be randomly divided into five groups, control group, group1 (100μg/kg/d, and the highest concentration of iron is ≤0.8g/100ml PN), group2（200μg/kg/d, and the highest concentration of iron is ≤0.8g/100ml PN), group3 (300μg/kg/d, and the highest concentration of iron is ≤0.8g/100ml PN), group4 (400μg/kg/d, and the highest concentration of iron is ≤0.8g/100ml PN). Iron supplementation period for more than ten days. For five groups, complete blood counts, differential counts, and reticulocyte counts were measured weekly in samples obtained, serum iron, iron protein, total iron binding force were measured at baseline and after 2 weeks. Through comparative analysis of five groups, to find iron-fortified PN whether affect anemia rate and iron storage in premature infants. The investigators also selected malondialdehyde (MDA) and 8-isoprostaglandin F2α (8-iso-PGF2α) as the investigators concerns about iron used in PN induces oxidative stress index. Iron protein determination use radioimmunoassay method, serum iron and total iron binding force determination use chemical method, MDA and 8-iso-PGF2α determination use enzyme-linked immunosorbent assay method.