The main challenge in predicting global responses of floating vessels in deepwater and ultra-deepwater areas comes from the system’s coupled effect.In this paper,the coupled approach is used to analyze effects of riser on floating system in deepwater.The analysis results show that the coupling effects of risers will mainly affect the low frequency (LF) motions of the system.That is because risers will provide the system with a significant low frequency (LF) damping which will vary with the sea states.Under storm sea state,the excitation term from drag force will govern the response.While under the moderate conditions,the damping effect of risers is more significant.In the practical engineering,the combination effect should be considered by other ways when the risers are omitted from the model. The main challenge in predicting global responses of floating vessels in deepwater and ultra-deepwater areas comes from the system’s coupled effect. In this paper, the coupled approach is used to analyze effects of riser on floating system in deepwater. The analysis results show that the coupling effects of risers will mainly affect the low frequency (LF) motions of the system. That is because risers will provide the system with a significant low frequency (LF) damping which will vary with the sea states. Under storm sea state, the excitation term from drag force will govern the response. Under damping the moderate conditions, the damping effect of risers is more significant. In the practical engineering, the combination effect should be considered by other ways when the risers are omitted from the model.