Reshaping berm breakwater is one of the types of rubble mound breakwaters that reshaped when attact with waves. In the present study in order to optimally design this type of breakwater, the cause of the reshaping in this study is to investigate the mechanism of reshaping in this kind of breakwaters. To achive this goal, using an OpenFoam software, an appropriate numerical model is created for the modeling of regular wave interaction with porous mediaModeling of flow in the breakwater is performed using flow resistance coefficients in porous media. The porosity medium coefficients were calibrated using an innovative method and laboratory data.The numerical model for the regular wave with a height of 0.145 meter and a period of 1.7 seconds for the profile before and after the structural reshaping respectively were performed and verified using laboratory results. Finally, to investigate the mechanism of structural reshaping of the berm breakwater the results of the numerical model and the experimental model are compared and analyzed. The results of the research indicated that the maximum value of the spatial variation of the positive pressure that causes the outward pressure force is occurred near the maximum occurrence of rundown of the current on the structure slope. On the other hand, simultaneously with the maximum spatial variation of positive pressure (outward directed gradient) creates maximum force due to outward flow from the structure that also located at the bottom of the stream along the structure. The geometry of the breakwater profile after the reshape has a milder slope than the initial profile, and the reshape profile creates a pond of water in front of the structure. Changing the slope and creating a water basin causing more waste the incident wave energy. The reshape caused to change the pattern of flow outside and inside the breakwater structure that leads decline active forces enterctive the armors.