Regarding the urgent need of ecological reef clearing，milling method as a mechanical rock excavation method is used in underwater reef clearing.According to the field test data of milling and clearing the reef，based on the discrete element 3DEC simulation of the process of milling and clearing the reef，this paper studies the reef breaking law of different construction parameters (output torque，working pressure，knife depth，swing arm velocity).The simulation results show that the output torque and working pressure have significant influence on the operation of milling head，the over-high working pressure leads to the clamping phenomenon of the milling head.Milling head stuck tool will increase cutting resistance and affect the life of the cutter.The specific energy consumption of normal operation of milling head decreases with the increase of output torque and working pressure.The cutting resistance and milling efficiency both increase with the increase of cutting depth and swing arm velocity.The specific energy consumption of reef milling decreases with the increase of the cutting depth and has an exponential decreasing relationship with the swing arm velocity.The research results have important reference significance for the actual construction of milling and breaking reef.