This study constructed a numerical simulation platform for the oxidation ditch (OD) system for wastewater treatment based on Bayesian inference approach, which was used for the simulation and process optimization. On the basis of simulator, IWA ASM2d model was employed to model two types of OD systems, and predict the nitrogen and phosphorus removal performance under current operational conditions. The model was calibrated by Bayesian inference approach. It shows that the calibrated model was reliable, and can be used for further optimization study. With the dynamic simulation, this study analyzed the kinetics and mass balance of nitrogen and phosphorus removal for the shallow ditch system. It indicated that the denitrifying phosphorus removal contributed significantly, and was predominant in the system. Meanwhile, the unique hydraulics due to the brush aerators leads to a DO spatial distribution, leading to substantial oxygen limiting conditions in the aerated zone, achieving simultaneous nitrification and denitrification as well as phosphorus removal. Based on the numerical simulation, this study selected aeration cost, sludge production and effluent violation as criteria, and proposed two non-dimensional unified cost index and performance index for the process assessment and operational strategy optimization. Scenario analysis was performed on the aeration and sludge discharge strategies to suggest optimal strategy with high efficiency and low costs. The optimal strategy for shallow ditch system was: 8 aerators for March to October at 15°C above, 10 for other periods, and 250 m3/day sludge discharge. This could achieve ammonium and TN effluent violation lower than 5% and 2% respectively, saving 12% of aeration costs, and reducing sludge production by 2%. As for the deep ditch system, optimal strategy was: 5 aerators with the mode 111100100, and 200 m3/day sludge discharge, which could achieve less violations of ammonium and TP (10% and 30%), saving 46% aeration costs without remarkable increase of sludge production. In addition, the kinetic analysis for deep ditch system show that adjusting the aeration strategy means to change the anoxic/aerobic HRT, oxygen supply, and DO spatial distribution, leading to significant shifts of key kinetics behaviors.