An integrated OCO reactor with two side-ditch separators based on the anaerobic/anoxic/oxic (A2/O) process was developed for municipal wastewater treatment in this study. The effects of dissolved oxygen (DO) concentration, hydraulic retention time (HRT) and the ratio of chemical oxygen demand (COD) to total nitrogen (C/N) in the influent were investigated for optimization, in order to achieve the removal of total nitrogen (TN), total phosphorus (TP) and COD in the reactor simultaneously. When the DO concentration of 2.0 mg/L in the aerobic zone, HRT of 12 h and C/N ratio of 8:1 were applied in the reactor, the superior removal efficiencies of COD, TN and TP reached 96%, 81% and 92%, respectively. The modification in integrated OCO system was characterized by the mixing of the liquid refluxed from anoxic and aerobic zones with the influent in the anaerobic zone. And the risk of activated sludge bulking was decreased successfully by enhancing phosphorus removal without any chemical auxiliary methods. Quite precise prediction results with the correlation coefficients (R) of 0.9584-0.9948 were forecasted by the back-propagation neural network model. All the results indicated that the integrated OCO process is able to remove TN, TP and COD in a reactor simultaneously.