Coagulation-ultrafiltration (C-UF) is wvidely used for surface water treatment.With the removal of pollutants,the characteristics of organic matter change and affect the final treatment efficiency and the development of membrane fouling.In this study,we built a dynamic C-UF set-up to carry out the treatment of micro-polluted surface water,to investigate the characteristics of dissolved organic matter from different units.The influences of poly aluminum chloride and poly dimethyldiallylammonium chloride (PDMDAAC) on removal efficiency and membrane fouling were also investigated.Results showed that the dosage of PDMDAAC evidently increased the UV254 and dissolved organic carbon removal efficiencies,and thereby alleviated membrane fouling in the C-UF process.Most hydrophobic bases (HoB) and hydrophobic neutral fractions could be removed by coagulation.Similarly,UF was good at removing HoB compared to hydrophilic substances (HiS) and hydrophobic acid (HoA) fractions.HiS and HoA fractions with low molecule weight accumulated on the surface of the membrane,causing the increase of transmembrane pressure (TMP).Membrane fouling was mainly caused by a removable cake layer,and mechanical cleaning was an efficient way to decrease the TMP.