Objective: The aim of this study was to develop a model to predict massive hemorrhage during cesarean section in pregnant women of previous cesarean section with placenta previa. Based on this model, we developed an equation of massive hemorrhage in pregnant women of previous cesarean section with placenta previa. Methods: We retrospectively reviewed 218 patients with previous cesarean section and placenta previa who underwent cesarean section from January 2011 to December 2021. Massive hemorrhage was defined as a blood loss exceeding 2,000 mL during operation. The data was analyzed by independent t-test, Pearson chi-squared test. Multivariate logistic regression analysis was used to develop a predictive model and identify factors predictive for massive hemorrhage. Results: A total of 53 patients (24.3%) had massive hemorrhage. Number of parity, anterior placenta, presence of lacuna, abnormalities of uterine serosa-bladder interface, extension of placenta into myometrium, serosa and bladder were selected predictive factors to develop a model to predict massive hemorrhage. Based on this model, an equation was developed and tested for performance. This model using five predictive factors yielded an area under the receiver operating characteristics curve of 0.886 (95% confidence i...