Résumé : Floating offshore tidal current turbines are usually moored in the sea, which will endure the wind-wave-current load in a long term. Power production of the tidal current turbine will result in extra excitation force acting on the platform, which will make the motion prediction and positioning system design of the floating platform more complicated. In order to predict the motion response of a floating tidal current power station, a coupled motion prediction method is established to explore the coupled interaction among the platform, the turbine and the mooring system. The turbine influence is considered as added mass and damping acting on the platform. Results shows that the fitted hydrodynamics agree well with numerical simulation results. The operation of the tidal turbine can increase the surge amplitude and pitch angle of catamaran, and the mooring line tension will increase as well. The research can provide some reference for motion response prediction and mooring positioning of a floating tidal current power station.