Abstract: This study employs the multiple-relaxation-time lattice Boltzmann method (MRT-LBM) coupled with the Shan–Chen multiphase and multicomponent model to systematically elucidate the influence of initial water saturation, waterflood front position, slug size, and water-to-gas slug ratio on the dynamic occurrence and migration patterns of multiphase fluids. The findings reveal that, across different water–alternating–gas (WAG) injection schemes, the proportion of injected water exerts a decisive impact on flow resistance, thereby reshaping the displacement pathways of both water and gas phases. Specifically, low water-to-gas ratios lead to discretely distributed water slugs, which enlarge the gas-phase sweep region and enhance displacement efficiency, although the risk of gas channeling remains. Conversely, high water-to-gas ratios contribute to a more stable displacement front but restrict the mobilization of the oil phase. These results uncover the microscale seepage mechanisms governing CO₂ WAG flooding in tight reservoirs, establish a robust theoretical foundation for optimizing development parameters to mitigate gas channeling, and offer valuable guidance for achieving more efficient field-scale oil recovery.