<p>The interaction between extreme waves and structures is a crucial study area in marine science, as it significantly influences safety and disaster prevention strategies for marine and coastal engineering. To investigate the flow field of a semi-submersible against extreme waves, a model simulating solitary wave interactions with the semi-submersible system was developed via the meshless smoothed particle hydrodynamics (SPH) method and Rayleigh’s theory. Notably, the wave surface and wave load results obtained from the SPH model, compared with those of OpenFOAM, result in an interaction test case between solitary waves and partially submerged rectangular obstacles and show good agreement, with a maximum relative error of 3.4%. An analysis of the calculated results of the semi-submersible facing solitary waves revealed several key findings: overtopping, which decreases with increasing water depth, occurs on the structure when the non-submerged ratio is 0.33 and the wave height surpasses 0.2 m. The transmission coefficient decreases with increasing wave height but increases as the water depth increases. Furthermore, the reflection coefficient peaks at a wave height <i>H</i>₀ = 0.2 m. The dissipation coefficient displays a valley trend with a small water depth, whereas it increases monotonically with increasing water depth. The dissipation coefficient decreases with increasing water depth.</p>