Abstract: In this paper, the 3-D liquid-filled tank is considered as aFluid-Structures Interaction (FSI) system that consists of the ideal,compressible fluid with free surface and the linear, elastic solid withthin thickness. This system is simulated with Finite Element (FE)method. In the FE model, the liquid is discrezied by pressure bodyelement and the tank is characterized by displacement shell elements.Since the coupling equation of this FSI system is unsymmetric, Arnoldi'smethod is adopted to get the dynamic characteristics of theliquid-filled tank. In addition, the shift-frequency technique isintroduced to solve the problem of zero frequency and an iterationmethod is adopted to make the computation both accurate and economical.A numerical simulation of a liquid-filled tank is carried out to confirmthe effectiveness of these methods.