Indonesia, with its geographical position in a tectonically active region, is highly vulnerable to tsunamis. The last tsunami to hit Indonesia, the 2018 Sunda Strait Tsunami, exposed the limited protective infra-structure in coastal frontal areas such as seawalls. These hard structures play a role in reducing the run-up and arrival time of tsunamis farther inland and their success is influenced by the elevation of the structure and the scale of the tsunami. This study aims to evaluate the effectiveness of seawalls in mitigating tsunami impacts under various wave height scenarios. The numerical simulation uses the Smoothed Particle Hydrodynamics (SPH) method implemented through DualSPHysics. The model was designed at a scale of 1:25, consisting of an upstream zone and a downstream zone. Modeling variations focused on the water level in the reservoir (Ho) of 0.4, 0.5, 0.6, and 0.7 m. The simulation results show that the seawall is able to reduce the impact force on the building up to 80%. The effectiveness of the seawall increases at lower ratios of water head to building height (Ho/Hb). The presence of the seawall also causes a delay in wave travel time of about t(g0.5)/Hb0.5 = 5.5 to 9.0. These findings have important implications for the development of coastal protection and disaster risk management strategies in tsunami-prone coastal areas.