Abstract: Activated sludge method is mainly used to sewage water treatment of water injection system in oil field,dissolved oxygen of sewage pond plays a crucial role during the process of sewage water treatment.The design of PIDdissolved oxygen control algorithm is developed based on first order plant model,and the parameter regions of the robust stability can be determined by using a graphical approach.Simulation results are provided to illustrate the design procedure and the effectiveness of the proposed methods.When applying to the wastewater treatment system based on activated sludge,this method can make the sludge maintain good performance,and is of great robustness.Simulation results are provided to illustrate the design procedure and the effectiveness of the proposed methods.