Abstract: Simplifying the floatation ring which is one of very important components of the deep-water anti-storm wave cages into a flexible ring, we obtain the nonlinear governing equations of the out-of-plane motion and deformation of a circular ring based on the fluid-structure interaction theory. The mode superposition approach is utilized to solve the equations, and the motion and deformation of the ring are numerically computed under the actual action of water waves. The computational results have shown that the deformation of the ring can not be neglected in the first three modes, and that the effect of the fluid-structure interaction is significant.