This study investigates the wave-induced flow inside and outside a rectangular porous offshore structure, which is induced by the interaction between water waves and porous media. Threedimensional experiments have been conducted to measure flow fields around the structure. Numerical simulation has been carried out to investigate the mechanism of wave-induced flow field and governing physical parameters, as well as behavior of water particles inside porous structure. Results of waveheight distribution and Eulerian velocity field show fairly good agreements between numerical and experimental models. It has been confirmed that flow field is strongly affected by wave period. Other parameters such as media diameter, porosity, and resistance coefficients have been shown to affect the flow field, however, its degree depends on the wave period.