Tertiary oil recovery sewage in Bohai oilfield contained anionic polymer， which had space steric effect. The traditional polyether block type water-clearing agent had a slow water-cleaning rate， large dosage of reagents， and a large number of sticky flocs adhering to the wall of pipeline and causing blockage of device. With epichlorohydrin and organic amine as the initiator， and ethylenediamine as the crosslinking agent， a new high-efficiency quaternary ammonium cation water clarifier H1 was synthesized by controlling reaction condition. The clear water effect of H1 and detergents（BHQ-04 and BN-5）used in field was compared. The results showed that water clarifier H1 had the best water-cleaning effect which synthesized on the condition of 1.2∶1∶0.3 the molar ratio of three ingredients（epichlorohydrin∶organic amine∶crosslinking agent）， 5—6 hrs reaction time and 75℃. The effective purifying concentration of H1 was only 175 mg/L， which was far lower than that of BHQ-04（400 mg/L）and BN-5（300 mg/L） . Compared with BN-5 and BHQ-04， H1 had higher oil-water separation speed and better flowability， and the upper flocculent was loose and free flowing after oil and water separation. The synthesized water clarifier H1 had the ability to prevent the formation of sticky silt during effluent treatment of polymer flooding in SZ36-1 reservoir of Bohai oilfield