Ferric chloride (FeCl3) and polyacrylamide (PAM) are used as flocculant and coagulant aid for treating the dredging wastewater from Chongqing Liangtan river. The effects of dosages of flocculant and coagulant aid on removal rate of turbidity, suspended solid (SS) and COD were investigated. The effects of Zeta potential and particle size distribution on treating performance were also discussed. It was found that the optimal flocculation performance was achieved when the absolute Zeta potential approached zero. Lower dosages of flocculant and coagulant aid were needed when the average particle size of SS in dredging water was smaller.