It is known that the effect of fluid vibration upon structural one is very large, therefore fluid-structure coupling analysis method which combine the added mass matrix into FEM have been used since many years ago. But there has been no approach to such analysis method using experimental modal analysis. It is necessary to estimate vibration level on actual ships, and to examine the validity of the FE models. In this paper, a new idea of reduced added mass matrix is defined and described completely, and the validity of the idea is verified by comparing with Matsuura's theory. Then combination analysis of the experimental modal analysis and BEM is described using the reduced added mass matrix, and the validity of the combination analysis method is verified by comparing with some experiments in the deep water and the shallow water. As the result of the validity, vibration level on actual ships in the deep water can be estimated by using this new method.