The oil-water interaction in water-flooding is scarcely studied and the existing conclusions are controversial，which is mainly reflected in a lack of a unified conclusions of potential determining ions on oil-water interaction. Experiments on coreflooding and interfacial tension measurement were combined to study the oil-water interaction law and mechanism in smart water-flooding. The results show that oil-water interaction plays an important role in smart water-flooding，and adjusting the ion composition of the injected water can considerably influence recovery factors. Mg2+ and Ca2+ can effectively improve coreflooding efficiency，of which Mg2+ performs better, and they both have optimal concentrations. SO42- has no positive effect on enhencing recovery factors. According to interfacial tension measurement，the effects of ions in the solution on the characteristics of the oil-water interface vary enormously in the intensity order of Mg2+ > Ca2+ > Na+. As the concentrations of Na+，Ca2+，and Mg2+ increase，the oil-water interfacial tension goes down first and up then，and the interfacial relaxation time first shortens and then lengthens. There are optimal concentrations that lead to the lowest interfacial tension and the shortest interfacial relaxation time. SO42- can effectively inhibit the influence of Na+，Mg2+，and Ca2+ on the characteristics of the oil-water interface，increase optimal ion concentrations corresponding to the lowest oil-water interfacial tension，and extend the time for the oil-water interface system to reach equilibrium.