Hydrodynamic analysis of a moored semi-submersible type offshore wind platform has been carried out. Three methods are used in this study. The first method is the wave tank experiment with a 1/50 scale model which is carried out in the towing tank of RIAM, Kyushu University. Wind is not considered in the experiment and the mooring system is approximated by a spring system. The second method is the CFD simulation, which is performed by using our in-house research code RIAM-CMEN. This code is a based on a multi-phase Navier-Stokes solver for prediction of strongly nonlinear wave and wind loads on a floating body in rough sea conditions. The third method is a potential flow based numerical model, in which hydrodynamic loads on the floater are solved by the potential flow theory, the mooring lines by the catenary theory, and the aerodynamic loads on the wind turbine by the blade element momentum theory. This method is used as a practical analysis tool for parametric study. In this paper, numerical results are compared to the experimental data and discussions on these analysis methods are presented.