Sloshing in a liquid tank of huge size could potentially induce the structural vibration and fatigue damage. Though many numerous researches of sloshing have been conducted to characterize the impact phenomenon, the problem still remains to be addressed since the neglect of hydro-elastic behaviors of structure which will presence in the real phenomenon. In this paper a hybrid method has been developed to study the three-dimensional (3D) liquid sloshing with the consideration of structural elasticity. The improved moving particle semi-implicit (MPS) method is employed to simulate the evolution of 3D flow. The finite element method (FEM) is employed to calculate the vibration of the flexible tank wall. The MPS and FEM methods are coupled with a partition strategy within the fully Lagrangian system. Then, the sloshing in a 3D elastic tank is numerically investigated and results are compared with those corresponding to a 3D rigid tank. The effects of the structural elasticity on the sloshing behaviors are discussed.