A 10 MW floating offshore wind turbine (FOWT) is developed by a Korea R&D project. The FOWT is composed of three blades, a tower and their supporting floater. Three catenary steel chains are attached to the floater for mooring lines. The design target site is East-South sea of Korea. Since the FOWT is a floating structure in waves, evaluation of hydrodynamic behaviors is a key process in design of FOWT. This paper carried out hydrodynamic analysis for the FOWT to evaluate its responses in waves, winds and currents. Wave forces at floater were analyzed by higher order boundary element method (HOBEM) and the catenary behaviors of mooring lines were analyzed by finite element method (FEM). The time domain body-mooring coupled responses were calculated by convolution method and the floater motions and mooring line tensions were obtained from the coupled analysis. Experimental model test was also carried out in ocean engineering basin in KRISO. Floater motions and mooring line tensions were measured from the model test and all the results were compared with the numerical results.