This paper presents a simplified model for the dynamic analysis of a floating off-shore wind turbine (FOWT), which can be suitable for early feasibility and pre-engineering studies, where the complete system has to modeled in order to predict its behavior and to assess the performance. The model solves the equation of motion in time domain and considers Morison equation for computing the hydrodynamic loads. The aerodynamic loads are included by considering the wind thrust at hub height and the loads from the mooring system have been computed as a non-linear model. A methodology is also presented for calculating the structural properties of the system. The model is tested for two load cases and compared to results obtained with the more complex model FAST. The comparison between the response of the models is satisfactory. The simplified model allows to capture the main motions of the FOWT with an acceptable accuracy. A further feature of the model is to calculate the power generation of the floating wind turbine. The results show that the losses in comparison with a bottom-fixed off-shore wind turbine are below 1% or 1.1% according to the load case, which confirms the good performance of the studied FOWT.