A fully coupled nonlinear simulation tool using Morison's equation is developed to predict the dynamic response of floating offshore wind turbine (FOWT) system. Water tank tests are conducted to investigate hydrodynamic coefficients and the performance of the simulation tool under different sea states. Three issues are discussed in this paper. First, correction factors for the added mass and drag coefficients are proposed to account for the effects of frequency dependent hydrodynamic coefficients, and the effects of these correction factors on the global matrices are validated by the forced oscillation tests. Then, the effects of the frequency dependent hydrodynamic coefficients and the axial Froude-Krylov force on slender members are clarified by the free decay tests and water tank tests with regular and irregular waves. Finally, the dynamic behavior of mooring system on the fairlead tension is investigated by using quasi-static and dynamic models, respectively. The dynamic responses of FOWT with improved hydrodynamic models agree well with those measured in the water tank tests. (C) 2018 Elsevier Ltd. All rights reserved.