In this paper, the motions are studied of a multi-body which is composed of two plates hinged together and mooredby eight mooring lines in regular waves. The experimental results are compared with computational results. The linear po-tential theory and the perturbation method are combined to study this complicated system. The former is used to calculatethe wave forces acting on the plates and the motion responses of them, while the latter is used to describe the dynamiccharacter of the eight mooring lines coupled with the two hinged plates. Some response results of each plate are presentedand comparisons between calculated results and experimental data are given. All the calculations are confined to regularbeam waves.