Abstract: Vortex induced motion（VIM）is an important cause for fatigue damage of the mooring system of floating structures. The present work studies the suppression effect of the splitter plate on the VIMs of the Spar-type floating offshore wind turbine（FOWT）through model tests and numerical simulations. The influences of the length of splitter plate L/D on the VIM characteristics are focused.It is found that at the splitter plate length of L/D = 0,the intensification of vortex-induced responses with the increased velocity manifests three sub-stages（i.e.,upper branch,lock-in region and desynchronization）and the vortex-induced resonance occurs. When the splitter plate length is L/D ≥ 0.2,the vortex-induced resonance does not occur anymore,and more specifically,the suppression on VIMs reaches over 70% when the splitter plate length is L/D ≥ 0.4. It is also found that the splitter plate can induce yaw motions of the Spar-type FOWT. Results show that the splitter plate has a significant suppression effect on the VIMs of Spar-type FOWT.