For the vibration analysis of floating structures, fluid-structure coupled analysis method which combine the added mass matrix into FEM has been used since many years ago. However, this method has some problems.To solve those problems, reduced added mass matrix method was proposed and this method needed the rotation vector for vibration analysis of higher order modes. In this paper, the method of extracting rotation vector in experiment is used by MCE (Modal Coordinate Expansion) method. The modal structural modification analysis is done by using the eigenvectors in 6 directions which contain the extracted rotation vector. This calculation is compared with the experiment in water condition, and the importance of eigenvector on fluid-structure coupled vibration analysis is shown.