To address the issues of high energy consumption, suboptimal oxygen utilization in the aerobic tanks, and sludge sedimentation and aging in current anaerobic-anoxic-oxic (A²/O) processes, the aerobic tank structure of the integrated sewage treatment device was optimized. Under the same aeration intensity, the oxygen mass transfer characteristics between micro-pressure internal circulation and conventional aerobic tanks were comparatively studied, and the internal flow field characteristics were analyzed. After stable operation of the unit, the effects of hydraulic retention time(HRT) and air-lift reflux ratio on effluent quality were investigated. Results showed that under the same aeration intensity, the total oxygen transfer coefficient K_La(20) of the micro-pressure internal circulation aerobic tank is approximately 1.16 times that of the conventional aerobic tank. The oxygen transfer efficiency (E_O2) is increased by over 10%, whereby the oxygen mass transfer rate and utilization efficiency are significantly improved, and energy consumption is reduced. Analysis of liquid phase velocity, vorticity distribution, and large-scale vortex structures further demonstrate that the micro-pressure internal circulation structure could optimize oxygen utilization, improve sludge sedimentation issues, and enhance water treatment efficiency. Under the conditions of HRT of 14 h and stripping reflux ratio of 250%, the integrated unit has good shock resistance performance and is suitable for chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (total phosphorus). The average removal rates of TP are 91.02%, 79.31%, and 77.77% respectively. The average effluent COD and TN concentrations met the first-level A standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB 18918—2002), and the TP concentration reached the first-level B standard. This research provides new ideas for enhancing oxygen mass transfer and reducing costs while improving efficiency in sewage treatment.