The paper mainly discussed the PAC,FeCl_3 and Al_2(SO_4)_3 coagulant effect on the potato starch wastewater.All of the indexes of the wastewater before and after the treatment,and the costs were analyzed synthetically.The results showed that Al_2(SO_4)_3 was the suitable coagulant to concrete the potato starch wastewater.On condition that the optimum dosage of Al_2(SO_4)_3 was 500 mg/L,the COD removal rate achieved 34%.