Water-flooding reservoirs are the mainstay in developing mature oilfields in eastern China，and they have entered the ultra-high water cut stage as a whole after long-term water injection development. Laboratory studies and field practice show that there is still potential for significantly enhancing oil recovery. However，the difficulty of scientific and efficient development has increased due to the heterogeneity of reservoirs and development dynamics， and further research is needed to enhance oil recovery technology. Uncompartmentalized reservoirs face challenges such as severe extreme water consumption in the later stage of ultrahigh water cut，affecting stable production and enhanced oil recovery through water flooding. Therefore，the theory of high water consumption zones was deepened， and the development technology of near-resistance layer recombination，the vector development technology of ultra-high water cut reservoirs， and the development technology of flow field adjustment in the later stage of ultrahigh water cut were developed through innovation，achieving water consumption control and reduction，with an average oil recovery of 43.7%. In response to the characteristics of fault block reservoirs with numerous faults and small fault blocks，as well as the challenges of small remaining oil reserves and difficult exploitation during the ultra-high water-cut stage， understanding of the accumulation patterns of remaining oil and hydrodynamic regulation mechanisms was deepened. A series of leading development technologies were developed through innovation， such as artificial peripheral water flooding and stereoscopic development， improving reserve control and water flooding efficiency， with an average oil recovery of 29.4%. These technologies have supported the stable and profitable production of fault block reservoirs. Given the poor physical properties of low-permeability reservoirs and the difficulty of effective water flooding， nonlinear flow mechanisms and pressure flooding development mechanisms were researched， supporting development technologies were formed， and the development limits were constantly broadened. A series of differential development technologies have been innovated， such as water injection of simulated horizontal wells in ultra-low permeability reservoirs，well pattern adaptation for enhanced oil recovery in general low-permeability reservoirs， and pressure flooding in lowpermeability and tight reservoirs， with an average oil recovery of 15.7%， realizing rapid and efficient development of lowpermeability reservoirs. Through the above technical research， the efficient development of water-flooding reservoirs in ultra-high water cut stage is realized. According to the development characteristics and situation of different types of reservoirs， the directions for further enhancing oil recovery of water-flooding reservoirs are being put forward.