Abstract: To complete high quantity arsenic disposal process in groundwater,after As(Ⅲ) oxidized into As(Ⅴ) by biological filter effectively,the optimal conditions for compound coagulants to remove As(Ⅴ)were conducted. Under the condition of As(Ⅴ) in the raw water of 2 mg/L,iron-aluminum compound coagulants were better than the single coagulant such as the iron salt or the aluminum salt for the removal of As(Ⅴ),which could save more than 50% adding. Besides,compound coagulants improved the absorption and sedimentation performance for As(Ⅴ) and sedimentation performance for floc. For the trace of As(Ⅴ) in the effluent,Al played more important role in As removal and cross interaction for the two coagulants was also prominent. When combined the iron trichloride(5 mg/L) with the polymer aluminum sulfate(3mg/L),the effect of arsenic removal was the best. The optimal conditions for the compound coagulants show that when pH is 6. 00- 7. 00 and turbidity is more than 30 NTU or less than10 NTU,the efficiency of compound coagulants for removal of the arsenic is the highest,which is stable to meet the request of the national hygienic standards for drinking water(10 μg/L).