To address polymer flooding emulsion in high water cut crude oil demulsification and oil-water separation, the bottle test method for the screening of a class of polymer containing liquid oil-water separation was used and the oligomeric quaternary ammonium salt I was found to show excellent demulsification performance, When ammonium salt I was added with the concentration of 25 mg/L, and the emulsion was demulsificated at 55 ℃ for 60 min, the dehydration rate reached 96.5%. Compared with conventional polyether or polyamines demulsifiers, the quaternary ammonium salt I made the solution clearer and oil-water interface neater. The mechanism of the quaternary ammonium salt I affecting the emulsion was studied with optical microscope, dynamic analyzer and contact angle analyses. It was shown that free water in the oil droplet coalescence separation zone accounting for a leading role was instable and the emulsion oil droplet moved upward when oligomeric quaternary ammonium salt I was added to polymer flooding produced water. Being immersed, the solution of ammonium salt I on the surface of the pore core turned to water wet state. The result showed that changes of the interfacial wettability of the pore core on the membrane emulsification of strong dissolving capacity might lead to the rupture of the liquid film and oil-water separation. The contact angle measurement showed that the salt I of the liquid surface of the emulsion changed to water wet state, the strong wettability of the emulsion film was caused by the change of the film breakup, and the oil water was successfully separated.