The simulations of nonlinear sloshing in both two-dimensional and three-dimensional liquid tanks with porosity girder are carried out in time domain by using the Multi-domain Boundary Element Method (MBEM). The comparison of the present results and the references is conducted and shows they agree well with each other. The three- dimensional effect and the influence of the width of liquid tank and the height and porosity of the girder on the natural period of the model are also discussed.