With aluminium chloride and ferric chloride as raw materials,a series of inorganic polymer coagulants-polyalu-minium ferric chloride（PAFC） with different amount-of-substance ratio of Al/Fe and basicity were prepared,and then used in coagulation process of surface water.The coagulation efficiency and floc characteristics of PAFC were studied to optimize its application conditions,and meanwhile coagulation mechanisms were also analyzed.Results showed that synthesized PAFC possess a variety of hydroxy bridged aluminum-iron polymers.Colloidal particles became destabilization due to the charge neutralization mechanism of PAFC hydrolysate,and then the bridge between hydroxyl and oxygen could promote the bridging and sweeping precipitation action.The coagulation effect was excellent.The pH range of PAFC was wide,but the amount-of-substance ratio of aluminum to iron had a great influence on the hydrolysis process.The amount-of-substance ratio of Al/Fe was 7:1,the alkalinity was 0.5 and the dosage was 10 mg/L.Under the conditions,particle size and growth rate of flocs were the largest,and the removal rates of turbidity and UV₂₅₄ reached 84.93% and 78.52%,respectively.In addition,coagulation efficiency of PAFC was greatly influenced by hydraulic conditions.The optimum parameters were as follows：the fast stirring time was 20 s,the fast stirring speed was 200 r/min,the slow stirring time was 15 min and the slow stirring speed was 40 r/min.