The invention relates to a method for separating and treating an emulsified liquid by a magnetic nanoparticle coupled membrane. The method comprises the specific steps that functionalized Fe3O4 nanoparticles are prepared; the functionalized magnetic Fe3O4 nanoparticles are prepared into a suspension liquid, the suspension liquid and the emulsified liquid are mixed and stirred to obtain a particle-emulsified liquid mixture; ultrafiltration and demulsification are carried out on the particle-emulsified liquid mixture through an ultrafiltration membrane under the action of a rotating magnetic field; and after the demulsification achieves oil-water separation, the functionalized magnetic Fe3O4 nanoparticles are recycled under the action of an external magnetic field. Compared with an emulsified liquid separated and treated by separate membrane, the flux of the treatment of the emulsified liquid is improved by 10.4 times, and compared with the disclosed Chinese patent CN106830431A, the fluxis improved by 2 times when the rotating magnetic field is not introduced. The method for separating and treating the emulsified liquid by the magnetic nanoparticle coupled membrane has the advantages that the membrane flux can be further improved, the filtration efficiency is improved, and the membrane pollution is retarded; the magnetic nanoparticles are cycled after being separated from oil, and the cost is reduced.