Abstract: Take the inverted A²/O process of the municipal sewage treatment plant as the research object, this paper introduced the basic situation, main design parameters and technical characteristics of the process, and analyzed water quality test data of the past two years. The results showed that the inverted A²/O process could effectively remove COD and BOD₅, and the function of nitrogen and phosphorus removal was notable. An optimal control scheme for the carbon source dosing point, the sludge external reflux ratio and the DO at the end of the aeration tank, was proposed. In summer and autumn, the external reflux ratio of sludge was controlled in 60%~75%, the reflux ratio of nitrifying liquid in 100%~150%, and the DO at the end of aeration tank in 1.5~3.0 mg/L. In winter and spring, the external sludge reflux ratio was controlled in 120%~150%, the nitrification liquid reflux ratio in 200%~250%, and the aeration tank end DO in 3.0~5.0 mg/L, all of which could obtain better pollutant removal effect as follows: the effluent COD average value was 26.1 mg/L, the removal rate was 90.4%, the effluent TN average value was 7.69 mg/L, the removal rate was 78.1%, the effluent ammonia nitrogen average value was 0.445 mg/L, and the removal rate was 98.3%.Phosphorus removal was achieved by changing the addition point of phosphorus removal agents and building an automated chemical dosing system. Then the actual dosage of the phosphorus removal agent was reduced obviously to 2.5 t/d, and the TP average of the effluent was 0.194 mg/L, with a removal rate of 96.7%.