Owing to importance of seeking a proper stability evaluation of the rubble mound structure against the incident waves, a systematic study has been carried out to investigate the stability of a multi-layer berm breakwater. To have this fulfilled, an experimental study in a wave flume under irregular waves with JONSWAP energy spectrum and regarding an apposite range of sea state condition and geometrical parameters affecting MLBB’s stability has been conducted. In the current study, through the observation of profiles measured before and after each test, the effects of environmental parameters such as wave height, wave period, water depth and also a diversity of geometrical parameters including berm width, berm elevation from SWL, stone class I height, front slope and nominal diameter of stone class I over the eroded area, have been individually scrutinized and studied. Present results have given an account of the fact that the stone class I height affects the stability of ML. Results outlined that an increase in wave height, wave period, water depth and berm elevation from SWL would increase the damage parameter in ML. However, quite the contrary by enhancing the structural parameters like berm width, nominal stone diameter of stone class I and its height, results in a more stable structure opposing the incident waves. As another part of this study, we have delved into the interaction between waves and the structure through the experimental observations and a numerical modelling. Moreover, through the investigation of inside pressure changes caused by charging and discharging of the porous media and also the flow pattern in the course of maximum run-down, it has been determined that both positive pressure gradient oriented outwardly and the vertical force caused by the seepage flow from inside to outside have occurred simultaneously. In this study, a new dimensionless parameter is introduced to indicate that the wave breaking type plays a fundamental role in stability of ML. Eventually; a new formula is derived to estimate the damage of ML, based on a wide range of sea state conditions and geometrical parameters for to propose a practical use of the outcomes. Providing practical results, a novel approach among three different stability evaluation parameters such as damage level (Sd), the non-dimensional berm recession width (Rec/Dn50) and the nondimensional depth of the intersection point of the reshaped and initial profile is proposed. Furthermore, some applicable design recommendations to aid designers for berm parameters including berm width, berm elevation form SWL and the height of stone class I have been offered. Additionally, this formula is compared with the prototype data and Sirev?g MLBB’s results and thereby the Sirev?g breakwater has been redesigned and compared with the existing one using the given formulae and design recommendations. Key Words Multi-layer Berm Breakwater, Hydraulic Stability, Experimental Study, Numerical Modeling, Environmental Parameters, Geometrical Parameter