Abstract: The damping ratio is an important parameter in the research on fuel sloshing of spacecraft. In this paper, the liquid sloshing in the cylindrical container with rigid and elastic ring baffles are emulated by finite element method respectively, based on the hypothesis of ideal linear potential flow and the damping mechanism adopted in recent dissertations. Compared with the experiments of NASA, the frequency derived by the finite element method coincide with that of NASA well, while there is a considerable discrepancy with the damping ratio. Finally, the comparison of the flow fields of viscous liquid sloshing in a rectangle tank with a baffle and those without baffle emulated by ALE finite element method show that one important form of the "drag" that the baffle applying to the liquid is vortex. Key word：sloshing, frequency, damping ratio, baffle, tank, liquid-solid interactionALE finite element method