To protect the environment and improve the utilization rate of water resources is our goal of gas-making sewage treatment. In the settling tank, the micro-suspended particles in the micro-hazard flow clarifier, under the effect of reagent and vortex, increase rapidly and speed up the settling speed. In order to achieve the deep purification of circulating water, improve water quality and reduce water temperature, and finally achieve the goal of sewage “Zero”discharge. Taking a chemical fertilizer plant as an example, this paper summarizes the case of rebuilding the sewage treatment facilities of the plant.