This paper describes the equivalent mechanical and electrical models of vibration suppression systems using piezoelectric elements. All vibration modes of the host structure are included in the equivalent mechanical and electrical models proposed in this paper. Using these equivalent models, the coupling between the original vibration modes of the host structure can be considered. The equivalent mechanical and electrical models are theoretically derived. Using these equivalent models, not only the mechanism of the vibration suppression can be understood with ease but also simulations using conventional software become possible.