Abstract: Due to the influence of long?term scouring of injected?water, the physical properties and characteristic percolation parameters of reservoirs tend to change greatly in water?injection oilfields, which will result in large variations of relative permeability of rocks and more complexity of relative permeability curves after the changes. Conventional numerical modeling software never considers the variations of physical properties and relative permeabilities of reservoirs, so that the modeling results can’t match with the actual situation completely.A percolation mechanism model has been established for low?permeability Sha?20 fault block in eastern Subei basin to evaluate the changes of typical characteristic reservoir parameters during long?term water injection, by which the characterization of time?dependent numerical simulation method can be realized for physical properties and relative permeability of reservoirs. The result shows that long?term scouring of injected water will result in poorer physical properties and enlargement of the calculated average remaining oil saturation regarding medium and low permeability reservoirs, especially in the surroundings of injectors. But the remaining oil distribution patterns are basically the same before and after considering the time?depending effect