Abstract: Focusing on the difficult problems of unclear understanding of the mechanism of tapping the potential of remaining oil and the seepage characteristics in the ultra-high water cut stage of the bottom water heavy oil reservoir in Bohai Oilfield, this paper takes the main sand body of typical fluvial facies in Q oilfield as an example to carry out the experimental study on the ultimate water displacement efficiency of different types of reservoir samples under 2 000 PV high-multiple water displacement. The experimental results show that after high multiple water flooding at 2 000 PV, the maximum displacement efficiency of thin oil, common type 1 heavy oil and common type 2 heavy oil is 76.5%, 75.5% and 72.5% respectively. Under the same high-multiple water flooding conditions, the inflection point of the oil displacement efficiency of thin oil samples appeared at 100 PV, the inflection point of the common type 1 heavy oil samples appeared at 300 PV, and the common type 2 heavy oil samples appeared at 1000 PV. The greater the viscosity of formation crude oil, the later the inflection point appears, and the later the abandonment time of water flooding to the residual oil state. In the high multiple displacement process of 100～1000 PV, the oil displacement efficiency per PV of the common type 2 heavy oil samples, is higher than that of thin oil samples and the common type 1 heavy oil samples. Under the high multiple water displacement condition of 2 000 PV, the oil displacement efficiency can finally reach up to 72.5%. The experimental results can provide mechanism support for large liquid extraction and tapping potential of heavy oil with bottom water in the ultra-high water cut stage.