Advance Marine Vessel, Semi-SWATH is a potential vessel design for offshore operation. Fin stabilizer is an essential component for Semi-SWATH to handle the instability in rough weather. Therefore, the best design for the fin stabilizer should be chosen to ensure good Semi SWATH performance including optimum powering and seakeeping criteria in various conditions. However, seakeeping analysis of semi-SWATH in free floating condition is less available than in high-speed condition. The hydrodynamic analysis of the fin stabilizer on Semi SWATH vessel is very essential in free-floating condition to maximize the function of fins on Semi SWATH. In this paper, the hydrodynamic analysis of fin stabilizer for free floating semi-SWATH is analysed at zero degrees fin angle. In this research, the hydrodynamic of semi-SWATH is obtaining from CFD simulation. Analysis results indicate that reduction of pitch angle for free floating up until 9.8% is obtained with fin stabilizer for wave length ratio 4.2