A porous-structure device includes a semi-submersible platform consisting of four columns, two pontoons, two horizontal supports and a deck. Fillets on middle portions of the columns have a square section, a radius of the fillets, close to the deck and the pontoons, of the columns is gradually decreased to 0, a porous device is disposed outside each column and is formed by combining and connecting four single components, and each single component is formed by combining and connecting a plurality of porous laminated plates and a plurality of connecting pieces. The parameters, such as the pore type, porosity, number of layers, interlayer spacing and installation height, of the porous laminated plates are set according to the wave characteristics in different sea areas.