In the current sewage treatment process of urban wastewater treatment plant, AAO (Anaerobic/anoxic/oxic ) biological pool occupies a pivotal position. It can achieve expected design effect of the nitrogen and phosphorus removal by setting appropriate online detection instruments in the AAO biological pool, using advanced PLC automatic control system, regulating the amount of aeration, returned sludge and other parameters. In order to adjust the design parameters of the AAO biological pool according to the water quality and temperature etc., by combining inverter, advanced automatic control technology and communication technology to control frequency of blower, returned sludge pump and so on, it not only can meet the requirements of process design, but also be a more energy-efficient technical means.