Objective To explore the risk factors of postpartum hemorrhage in cesarean section delivery women with scar uterus re pregnancy.Methods A retrospective selection was conducted on Medical records 263 puerperant who underwent scar uterus was followed by another cesarean section obstetrics department of Hangzhou Obstetrics and Gynecology Between August 2021 and December 2022.Whether to is postpartum bleeding,hemorrhage group(n=25)and non postpartum hemorrhage group(n=238)based on whether there was postpartum hemorrhage.Single factor and multiple factor Logistic regression models were used to screen for independent risk factors for postpartum hemorrhage in pregnant women who underwent cesarean section for scar uterine re pregnancy.Results The incidence of maternal PPH in 263 cases was 9.51% (25/263),showed that the postpartum hemorrhage group had significantly higher miscarriage frequency,history of magnesium sulfate for fetal protection,prenatal bleeding,combination of dangerous placenta previa,placental implantation or adhesion,and uterine contractions compared to the non postpartum hemorrhage group(P<0.05).The levels of prenatal hemoglobin and fibrinogen were lower than those of the non postpartum hemorrhage group(P<0.05).Logistic regression analysis:The number of abortion≥3(OR=3.122),prenatal fibrinogen≤3 g/L(OR=2.510),dangerous placenta previa(OR=7.903),uterine atony(OR=4.096),and uterine incision tear(OR=5.831)Is a risk factor for maternal secondary cesarean section with PPH.Conclusion Avoid unintended pregnancy to reduce the number of abortion,strengthen prenatal fibrinogen index monitoring,pay attention to the treatment of dangerous placenta previa and uterine contraction weakness,alert to the occurrence of intraoperative uterine incision tear,help to prevent and reduce the occurrence of severe postpartum bleeding.