The predominant flow channels are the root cause of the plane waterflooding imbalance and low sweep coefficient of well patterns in medium and high water cut oilfields. To accurately locate the development positions of dominant flow channels in a reservoir and guide the subsequent stabilizing oil production & controlling water cut in the oilfield，by the time-varying numerical simulation technology of reservoirs，this paper proposed a new flow-field evaluation index，i.e.，“the oil-to-flux ratio（OFR）”，and a flow-field heterogeneity evaluation index，i.e.，“the heterogeneity coefficient of OFR”，from the perspective of oil displacement efficiency by water. According to the shapes of OFR characteristic curves in different water cut stages and the physical background，the flow-field flow area is divided into four levels to achieve the hierarchical evaluation of the reservoir flow field. The verification reveals that the predominant flow channel area of the flow field is completely consistent with the test results of tracers，which proves the reliability of the flow-field evaluation method by OFR. This method was used to evaluate the predominant flow field in the offshore BZ Oilfield of Bohai Sea，formulate the flow-field hierarchical control measures and policies，and guide the deployment of measures for profile control and water shut-off，as well as controlling water cut of horizontal wells. Upon application，the heterogeneity coefficient of OFR is reduced by 5.6%，which means the flow-field heterogeneity is significantly improved. This method realizes the quantitative characterization of the predominant flow channels in high water cut oilfields.