Pointed to the complexity and necessity of residual water treatment from environmental dredging, the paper took a comprehensive method for residual water treatment, using biological, physical and chemical methods, let the residual water pass through biological sludge tank, settling tank and clarification tank. Poly-aluminium chloride flocculants were uniformly added in residual water by using the integral drug-feeding equipment. The water quality of the treated residual water can reach the second grade of Integrated Wastewater Discharge Standard (GB 8978-1996). The results show that the method for residual water treatment is effective. The method can ensure the residual water to meet the effluent standard and the environmental dredging project to continuously dredge at the same time.