Abstract: To exam the effect of coagulation conditions on organic removal efficiency and membrane fouling of the coagulation-ultrafitration process, Yellow Biver reservoir water was studied by using the static ultrafiltration device. Effect of flocculation time on organic removal, flocs characteristics and ultrafiltration characteristics during the ultrafiltration process was investigated in this study and membrane fouling factors were also analyzed. Results indicate that the dissolved organic matter (DOC, UV ₂₅₄) removal mainly attributes to the condensing process, the following flocculation process has no influence. Coagulation time had significant influence on flocs characteristics and membrane fouling, and both shorter and longer time had negative influence. The flocculation time of 10mins was in the range of optimum, at which the fractal dimension, the normalized flux, the total membrane fouling resistance and the cake fouling resistance up to their minimum. However the normalized flux decline was the biggest and the pore blocking resistance lay in the stable state. 20mg/L dosage of PAC and 10min of flocculation time is the optimal optimum coagulation conditions in coagulation-ultrafiltration process, while achieving a good flocs property and ultrafiltration characteristics. Insufficient and excessive dosage of PAC would have a great influence on coagulation, flocs and cake layer characteristics.