According to the main characteristic of the city's water affairs dispatchment, the structure of water affairs dispatchment based on rough sets theory was proposed. After each factors were considered synthetically, knowledge expression system was set up, and the water affairs dispatchment control regulation was reduced and acquired. To some extent, it's a new method of processing the uncertain information in the water affairs dispatchment. The example demonstrates that this method has reduced the dispatchment control, and its regulation acquired is of objectivity, so it can solve preferably the control problem of the city's water affairs dispatchment.