Abstract: In order to search for remaining oil potential areas in the late stage of ultra-high water cut and explore the enhanced oil recovery (EOR) mechanisms of different oil displacement methods, this paper carried out physical simulation experiment of 3D large model to analyze the variation of injection pressure and sweep efficiency and the distribution characteristics of remaining oil saturation in the process of high-expansion water flooding, surfactant flooding, polymer flooding, binary compound flooding and microsphere emulsifier flooding. It is indicated that EOR potential areas in the late stage of ultra-high water cut are the unswept remaining oil areas and the swept weak and moderate water flushed areas instead of strong water flushed areas. The sweep efficiency cannot be increased further if high-expansion water flooding or ultra-low interfacial tension surfactant flooding is continued, which verifies that their EOR potential is low. And it is necessary to adopt the combination technology of in-depth plugging control and micro-flooding control. Self-aggregating microsphere emulsifier flooding has the advantage of plugging, displacement, re-plugging, re-displacement, and it can increase sweep efficiency and recovery factor by 38.6 % and 19.1 %, respectively. Compared with polymer flooding and binary compound flooding, it is much better in terms of plugging capacity, sweep area and oil displacement efficiency and presents promising application prospect.