The method to perform coupling analysis of offshore floating wind turbines (OFWT) was developted by integrating hydrodynamic and aerodynamic modules in time domain. The Morison method was used for hydrodynamic computation of floating body and its mooring system, in which the relative velocity between structure elements and waves was implemented by the hybrid wave model with second order accuracy. Slender rods theories were applied to the mooring systems, and the wind turbine was modeled by the aero-elastic code-FAST. Loads and displacements were transferred between the submodules based mainly on floating body control equations in every time step by the Newmark- β method. Motion responses of a 5 MW 3 blades spar type OFWT was predicted with and without FAST to validate the combined program. A comparison of results from the available 3D linear potential flow method in a random sea condition shows that the code is capable of hydro-aero dynamic analysis of OFWT.