Objective To identify risk factors of posttraumatic stress disorder (PTSD) following childbirth and to provide evidence for early detection, diagnosis, and treatment of postpartum PTSD. Methods The pregnant women who hospitalized for delivery of a baby were invited to participate in this study. Data were collected on socio-demographic and obstetric variables, and on newborns during hospitalization, then PTSD was assessed using the PTSD Checklist-Civilian version at 42 days postpartum in the obstetric clinic. Results A total of 714 women completed the study, and the prevalence of postpartum PTSD was 9.52%. Multivariate logistic regression indicated that first childbirth, fear of childbirth, caesarean section were risk factors of postpartum PTSD (P<0.05,P<0.01). Conclusion The prevalence of PTSD at six weeks postpartum is slightly high. Medical personnel should pay more attention to primipara mothers, women with fear of childbirth, and women undergoing caesarean section, assess their mental state and take preventive intervention as early as possible.