Abstract: In this paper, the vibration and seismic resistance characteristics of the multiarch dam are discussed according to the calculation result of the Fuzilin Dam by modal synthesis. It may be seen that the modals of the multiarch dam are very dense and they are formed by the interaction of buttresses as the main components with their first modal. The global modals of the multiarch dam reflect the different arrangements and compositions of the sub modals of all buttresses and arches.The vibration or response to the earthquake of every buttress is the summary result of these arrangement and composition.the fundamental frequency of the multiarch dam is a frequency group. In this group, every modal possesses the contribution of the same class and can not be neglected.