To investigate the nonlinear fluid-structure interaction mechanisms between floating structure and hydrodynamic environment, and to elucidate the slamming pressure distribution characteristics of semi-submersible platform subjected to freak wave, this study conducted a numerical simulation using CFD methods to analyze the flow field properties of freak waves and the load characteristics on semi-submersible platform. The k-epsilon turbulence model and dynamic mesh technique are used to generate huge amplitude freak waves on the software Ansys Fluent. A series of pressure probes are set up on the platform column to monitor the change of the bang pressure and analyze the factors related to the change of the bang pressure from the flow field information such as vorticity and water quality point velocity vector. Research has found that freak wave slamming can result in horizontal loads of up to 2.93×10^5 kN and vertical loads of 2.35×10^5 kN, while also resulting in a pitching moment of 6.55×10^6 kN·m. The intense fluid motion induced by freak waves may also cause uneven pressure distribution on platform columns and significant wave run-up phenomena.