Due to the increase of intensive population and industrial enterprises in the past few years, a large amount of wastewater and solid waste generated have changed the PH, biological species and quantity of soil and sea. Sewage treatment can promote the coordinated development of economy, resources and environment, and play a very important role in alleviating the shortage of water resources, improving the utilization rate of sewage and improving economic benefits. Therefore, in order to alleviate the pressure of water supply and promote the balance of water resources, it is very necessary to use scientific sewage treatment system during the period of water supply shortage. In the PLC wastewater treatment system of most of the wastewater, there is no step about how to judge the wastewater treatment result. In this paper, we judge the sewage treatment result by judging the change of PH. However, due to the complexity of acid-base neutralization process in wastewater treatment process, it has serious non-linearity and hysteresis. So in this paper, a fuzzy adaptive PID control system is designed. It can realize the real-time monitoring of PH value more accurately.