Abstract: To accurately characterize the displacement degree and sweep efficiency variation of water-drive reservoir at high water-cut stage, a relationship among waterflooding displacement degree Ed, volumetric sweep efficiency Ev and water cut fw has been established based on previous researches about oil/water relative permeability variations at high water-cut stage, and the comparison of the method before and after the improvement has been conducted by taking Sanjianfang reservoir in Shanshan oilfield as an example. The results show that when the reservoir enters the high water cut stage, the fw vs. Ed curve goes from an up-concave shape to a down-concave shape and Ed changes faster with the change of the water cut ; the Ev vs. fw curve changes from a down-concave shape to an approximate flat shape and Ev changes more slowly with the change of the water cut. The variations of these parameters at the high water cut stage revealed by the study can reflect the underground status of the waterflooding, which is of great significance for the development performance prediction at high water-cut stage