Precisely controlling the amount of flocculant additive is the key technology of flocculation process in the treatment of intermediate wastewater of papermaking.Zeta potential can reflect the stability of colloidal particles,charac-terize the flocculation effect in wastewater treatment,and guide the addition of flocculants.An on-line measuring device for zeta potential is built based on the flow potential method,and the three-level control unit of field equipment unit-computer monitoring unit-execution unit is constituted.The experimental results show that the system can detect the zeta potential of the wastewater to be measured in real time,and use the ratio,integral and differential integrated controller to optimize the control of flocculant dosage,and the system has a good man-machine interface.