Abstract: Objective To explore the situation of postpartum depression and its related factors among mothers with preterm infants.Methods A cohort of premature infants were established in the Hefei city maternal and child health care institutions from September 2015 to September 2016. The mothers of these premature infants were followed up to postpartum 42 days-56 days. The mothers were investigated using EPDS and other questionnaires during the follow-up. Using nested case-control study method, 36 mothers with postpartum depression were selected as case group, 72 cases without postpartum depression matched the date of infant birth, habitual residence with case group and selected as control group. And t test, χ² test and conditional logistic regression analysis were conducted to analyze the related factors of postpartum depression among mothers with premature infants.Results The rate of postpartum depression among mothers with premature infants was 30. 8% (36/117). Multivariate logistic regression analysis showed that high prenatal stress (OR=4. 739, 95% CI:1. 230-18. 257), more hospitalization days (OR=1. 040, 95% CI:1. 001-1. 082) were the risk factors for postpartum depression, and high independence of family environment (OR=0. 598, 95% CI:0. 397-0. 901), good entertainment of family environment (OR=0. 789, 95% CI:0. 650-0. 957) were the protective factors of postpartum depression.Conclusion The higher the stress of pregnancy and the more days of preterm inpatient staying in hospital, the higher risks of postpartum depression. The independence and entertainment of family environmental was protective factors for postpartum depression. The targeted measures should be taken to prevent and reduce the occurrence of postpartum depression among mothers with preterm infants.