This paper presents recent experimental and numerical work on dynamic analysis and load prediction of a floating platform. A new offshore renewable energy platform is designed for the second stage on-sea experiment of Kyushu University. An experiment is carried out in the towing tank with a 1/50 scale model, to verify the hydrodynamic performance of the platform and to prepare a benchmark database for validation of the numerical simulation method. The in-house CFD code, RIAM-CMEN, is extended for numerical simulation of the platform in harsh sea conditions. Numerical simulation is carried out and validated against the experiment.