In this study, the characteristics of the propagation of dam-break wave through a porous structure in a water tank is numerically analyzed by using the three-dimensional numerical model (ANSYS CFX model). As results of comparison between the existing measured and simulated water depth distributions in and around a porous structure, the agreement is relatively well satisfied. Moreover, for the case of the presence in part of a porous structure in a water tank, the three-dimensional flow structure is numerically analyzed In general, compared with in the area with a porous structure, the abrupt variation of water depth occurs in the area without a porous structure. It is shown that the porous structure can play a role to decrease the abrupt variation of water depth.