In the middle and late stage of development of offshore heavy oil field, strong injection and strong production are mainly adopted. Under this kind of large volume of liquid scouring, the microscopic pore structure of reservoir and the efficiency of water drive oil are changed, which brings difficulty to understanding the law of water drive development in high water cut stage of oilfield. Through simulating long⁃term water flooding and scouring physical experiments, the variation law of each characteristic parameter of reservoir during the long term water flooding scouring process is studied. The results show that for high porosity and high permeability reservoirs after long⁃term water flooding, the porosity change is not obvious, permeability is obviously increased, and invalid circulation channels are easily formed. The characteristics of pore microcosmic change are obvious, the radius of pore throat increases and the seepage ability increases. With the increase of displacement ratio, the isosmotic point shifts to the right. When the water saturation is the same, the oil phase permeability increases, the water phase permeability decreases, the residual oil saturation decreases, and the oil displacement efficiency increases by nearly 10%. The research results have been used in the field test of 2 000 m3/d liquid production per well in offshore sandstone reservoirs with high water cut, which provides theoretical support for the formulation of development strategy in high water cut period of offshore oil fields.