Large quantities of residual water with contaminants are produced during the dredging project of Taihu lake, which will bring environment pollution without treatment. Combining the experiments with real engineering, water quality and the correlation between pollution indexes were detected and analyzed in this article. Through coagulation experiments, the removal effects of different flocculants were investigated, meanwhile the amount of flocculants and the setting time were determined. Experimental results showed that the correlation exists between SS, CODMn , NH3-N and TP, so the method of only controlling SS for water discharge target could not totally satisfy the requirement. The sedimentation time in storage yard influenced the removal effects on pollutions greatly, thus, the bottom sludge could not flow into sedimentation tank without staying in the storage yard. PAC was the best flocculant, and the solid suspension concentration could drop below 100 mg/L when the concentration is 50 mg/L and the coagulation time is 5 minutes.