After the application of a non?ionic polyether clear water agent in an oilfield in the Bohai Sea,the difficulty of dewatering crude oil in the downstream terminal treatment plant increased,and the water content of the outgoing crude oil frequently exceeded the standard.The Effect of nonionic polyether water clarifier on crude oil dehydration was researched,the reasons of difficulty in dewatering were analysed,and the emulsion could not be treated by conventional polyether demulsifier.Polyamines were synthesised from dimethylamine,dodecyl dimethyl tertiary amine and epichlorohydrin,while polyethylene?polyamines were used as cross?linking agents to synthesise polyamine copolymer emulsion breakers.The emulsion breaker can reduce the water content of the external crude oil to less than 0.5% at a concentration of 80 mg/L,and reduce the static dewatering time of the crude oil from more than 120 h to less than 48 h.This effectively solves the problem of excessive water content in the external crude oil of the terminal treatment plant.