The formation mechanism and mobilization potential of microscopic discontinuous residual oil is currently the key difficulty of increasing recovery in heterogeneous reservoirs at high water cut stage. Two-phase flow simulations in heterogeneous sandstone pores based on the N-S equation and fluid volume method (VOF) can be used for quantitatively investigating the flow dynamic of residual oil clusters. The results show that the continuity of remaining oil is affected by pore structure heterogeneity. In cores with strong heterogeneity, higher oil saturation and more unswept pores influenced by the low coordination number were observed. The trapped disconnected oil bubbles were hard to remobilize due to the greater resistance to flow. Moreover, the mobilization of residual oil is the result of the combination of capillary force and driving force during water flooding process. Pores with good connectivity are the potential breakthrough positions for oil phase. The increasement of driving force would further push the phase interface to move and form a combined force with the capillary force, and effectively remobilizing oil clusters. This study reveals the formation and remobilization mechanism of microscopic residual oil in the high-water cut stages, providing a theoretical basis for adjusting the late-stage development measures and program design of water-flooding reservoirs.