In this study, we investigate the effectiveness of submerged porous medium on reducing incoming wave amplitude using a Two-Layer Shallow Water Type model. A new formula for the wave transmission coefficient, which is a ratio of the wave transmitted amplitude to the incoming wave amplitude, is then derived from the model analytically. This coefficient is the main instrument for evaluating the effectiveness of the porous submerged breakwater. In addition, the finite volume method on a staggered grid is used to solve the model numerically. We then validate the numerical scheme by comparing simulation results to the analytical solutions and experimental data. The verified scheme is ready to be implemented to simulate and predict wave transmission coefficient over actual coastal areas. Further, we examine the effect of the dimension and characteristics of the porous medium on the wave attenuation. We believe that these findings would be beneficial in the design of a coastal protection system.