Due to unfit soil and water conservancy in some regions of China, conventional water treatment has showed some defects for the poor quality of water resource. Ultrafiltration (UF) by hollow-fiber membranes is in increasing development in the fields of drinking water purification. Coagulation/UF process can be used to treat poor quality surface water: the permeate quality is increased and membrane fouling is reduced. In this research, a streaming current detector (SCD) method was introduced to asses how coagulation affects membrane performance. Results showed that membrane performance was improved with the coagulant added to get the positive streaming current (SC) value, since with the positive SC coagulation removed more organic matters. In the coagulation/UF process, coagulation unit does not need to be controlled to get complete charge neutralization, the point of zero charge, because the ultrafiltration membrane has an excellent ability to remove particles and colloids.