To realize the scale application of floating wind turbines in medium depth sea areas and solve the problem of energy shortages, viability of the new 6 MW spar-type floating offshore wind turbine (FOWT) was discussed by using Sesam software and aero-hydro-servo-elastic simulation code-FAST software.The wamit files of second-order wave force were calculated by the former and the dynamic response coupling analysis in time domain was carried out by the latter.The motion response of each DOF under different incident angles of wave and the effect of the second-order mean wave force and the second-order slow wave drift force on the motion response of the platform, mooring tension force and nacelle acceleration were researched respectively.The results showed that the yaw motion of the platform became more obvious when the incident angle of wave increased, while the other DOFs motion were affected little.The second-order slow drift wave force had a significant effect on the heave motion, and could stimulate a larger pitch motion response and induce larger mooring force.Moreover, the delta-line mooring system could avoid excessive yaw response and the maximum mooring force was below the breaking tension.Finally, the whole FOWT system had an excellent survivability in the harsh sea conditions.