This study proposes a novel numerical model of fluid-soil interaction to investigate tsunami generation caused by submarine landslides. The approach integrates CADMAS-SURF3D/2F (CS2F) for free-surface flow modeling with Anura3D’s saturated soil solver. Material Point Method (MPM) was used to capture the complex interaction between soil and fluid. Experiments involving a sandy slope with an impermeable layer were conducted where slope failure was triggered by excess pore water pressure. By supplying water from the bottom of the slope, the effective stress in the lower sand layer was reduced, which resulted in a rapid collapse and subsequent wave generation. The numerical model reproduced the formation of an arc-shaped shear zone and the swift propagation of excess pore water pressure leading to landslide initiation. Experiments demonstrated slip-type failures triggered by elevated pore pressure beneath the vinyl sheeting, which acted as an impermeable layer, whereas simulations revealed slump-type failures governed primarily by dead weight. This difference underscores the importance of modeling fluid flow effects after initial slope failure. Overall, the developed model successfully simulated the key physical processes of submarine landslide tsunamis. The presented model is expected to offer insights into their complex mechanisms and provide a basis for improved coastal hazard assessments.