In view of the increasing prominent sewage problem, the sewage treatment distributed control system was designed combining the host computer configuration software MCGS with the lower computer of S7200 PLC controlling system. First the hardware structure and the working principle of the control system were introduced. Next the PLC software program was designed and the whole operation realtime automatic monitoring of the sewage treatment system through the MCGS configuration software could be realized. Finally, the overall simulation and debugging of PLC control system using computer simulation technology was achieved. Experiments prove that the system runs smoothly and has reliable performance, friendly manmachine interface, high level of automation, and the good market prospect and application value.