In April and May 2011 model tests have beenconducted in the Offshore wave basin of MARIN to calibrate andvalidate simulation codes for floating wind turbines. This paperreports on a numerical study of an offshore floating wind turbine(OFWT) and about the comparison of simulation results withexperiments at model scale. This numerical study aims toreproduce the physical model tests of a wind turbine installed ona floater tested in waves. Firstly the model test set-up isdescribed. Secondly, the hydrodynamic model of the floater ispresented together with the representation of the wind turbine.In this numerical study the diffraction theory is applied todetermine the response of the floater to waves from its geometry.Then the motions of the floater are simulated in time domainwhen the floater is exposed to waves. The motions resulting fromthe numerical study are compared to motions measured duringthe model tests. The outcome of this comparison is discussed inthe conclusion of this paper.