The ultimate recovery of the conventional waterflooding sandstone reservoir ranges from 35% to 50%. This paper illustrates the feasibility of further improving the displacement efficiency of waterflooding reservoirs at the extra-high water cut development stage based on previous laboratory experiments，field applications，and global oilfield development cases.The economically feasible ideas and methods including long-term and large pore volume（PV）waterflooding and low salinity waterflooding etc. for improving the displacement efficiency are discussed in waterflooding reservoirs after improving sweep efficiency measures，such as the cyclic waterflooding，shut-in old well sidetracking，upward and layered waterflooding in multiple layers，or new infill wells along fault planes. Laboratory experiments and field applications reveal that the wettability of sandstone reservoirs changes from the oil-wet to the water-wet，and the saturation of residual oil reduces after long-term waterflooding，which can improve the displacement efficiency. Mature oilfield development cases indicate that with favorable reservoir and fluid properties，the ultimate recovery can reach 70% when reservoirs with strong natural waterflooding are developed by natural energy，or that with weak natural energy are developed by waterflooding. It has been proven that technologies such as dump flooding，low salinity waterflooding，and injecting and producing through one well are economically feasible. A large number of developed wells and existing facilities in mature field provide a basis for improving the recovery at the extra-high water cut development stage. The application of long-term and large PV waterflooding that is economically feasible is expected to increase the ultimate recovery to 50%-70%.