Abstract: In order to simulate the flow process of dam break flow,a large eddy simulation model based on Lattice Boltzmann Method（LBM）is adopted to adapt the wall viscosity. The free slip method is introduced to deal with the wall fixed boundary conditions. The flow process of instantaneous total dam break and instantaneous local dam break flow is simulated. The energy dissipation effects of the two kinds of energy dissipation sills are compared. The numerical simulation results show that:the LBM-based numerical simulation method can accurately simulate the flow situation and velocity variation law of the fluid free surface in the instantaneous dam break flow evolution process. When the instantaneous local dam break reaches the obstacle at 0.38 s,the water depth around the obstacle climbs and flows around the obstacle,and the force of the flow on the obstacle reflects the instability of the flow;the flow breaks through the dam. When the barrier is set in front of the dam,the splashing degree and the water tongue is formed after the liquid impacts the obstacle can be observed obviously. According to the pressure generated by the fluid impacting the left wall under two different energy dissipation sills,it can be judged that the energy dissipation capacity of the porous barrier is better,and the strength requirement of the structure without porous barrier is higher under the flow force. The results can provide a reference for a further study of LBM method combined with VOF method to capture free surface deformation and splash.