Abstract: Objective A retrospective comparison of the pregnant women with vaginal delivery(VBAC) and cesarean section after primary cesarean section was conducted to find out the clinical factors affecting the success rate.Methods 186 cases with primary cesarean section met the criteria of TOLAC were included in the study. TOLAC was observed under strict clinical protocol. According to the patients with VBAC and the patients with cesarean section,the patients were divided into two groups,and the general situation and clinical outcome indexes were compared between the two groups.Results Among 186 cases for TOLAC,150 cases had fulfilled VBAC(80.64%),36 patients turned to cesarean section,2 cases had incomplete uterine rupture(1.07%) and none had neonatal asphyxia. There were 21 cases(14%) had lateral perineum section. There were no statistic difference between two groups in age,gestational age,preoperative estimation of fetal weight and real weight and the thickness of the lower segment layer of uterine. The VBAC group had higher Bishop cervical score(t=2.184 P=0.030).; and fewer oxytocin induced labor 28%(42/150) than those in the failure group 52.8%(19/36)(χ²= 8.087,P=8.087). Logistic regression analysis found thatoxytocin induced labor increased the risk by 2.89 times for failed VBAC,(95%CI 1.282-6.539). The normal range of thickness of the lower segment layer of the uterus was around(1.40 ± 1.15),the minimum value was 0.12 mm,and the 25% percentile was 0.2-0.3 mm.Conclusion Under the rigorous clinical management system,TOLAC is relatively safe practice,the success rate of VBAC in this study was more than 80%,uterine rupture rate was 1.07%,no serious neonatal asphyxia and postpartum hemorrhage,no cases of hysterectomy.Natural in labor is an important factor for the success of VBAC. The higher the cervical score,the higher the VBAC rate. The thickness of the lower segment layer of the uterus is not sensitive for predicting rupture of the uterus.