To address the problem of sediment accumulation in the lateral inflow forebay of large pumping stations that pumps water from sediment-laden rivers, taking a lateral inflow forebay of the Jingtaichuan Electric Power Irrigation Project in Gansu Province as the research object, FLUENT software was used to numerically simulate water-sediment two-phase flow under sedimentation conditions for different contraction wall configurations of the lateral inflow forebay based on the Realizable k-ε turbulence model coupled with mixture multiphase flow model. The results show that a high-velocity mainstream zone is formed in the center of the inflow forebay, and vortices of varying sizes are generated on both sides of the mainstream zone, forming two low-velocity recirculation zones. Affected by the flow field structure, these recirculation zone on two sides are high-concentration sediment areas, with the relative sediment concentration increasing significantly from the mainstream zone to the recirculation zone. The increase in relative sediment concentration with the water depth in the recirculation zones is more significant than that in the mainstream zone. As the contraction angle of the sidewall of the lateral inflow forebay increases, the area of the recirculation zone outside the mainstream zone decreases significantly, the sediment-carrying capacity of the water flow is enhanced, and the proportion of the high-concentration sediment areas is significantly reduced, effectively improving the sediment deposition situation in the forebay.