The fully-coupled aero-hydrodynamic simulations of a floating offshore wind turbine consisting of a NREL-5MW baseline wind turbine and a semi-submersible floating platform are conducted. The three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations are solved for the coupled aero-hydrodynamic numerical simulation. The in-house code naoe-FOAM-SJTU, which is based on OpenFOAM and overset grid technology and developed for ship and ocean engineering, is employed. Aerodynamic loads on wind turbine are predicted. With the directly viscous simulations, detailed flow information around the turbine blades is available. The coupling effect on the aerodynamics of wind turbine from the platform motion is investigated.