Abstract: In order to study the consequences of a tailings dam break in a mine in Guangdong, the dam break process is simulated.The tailings dam is designed in two phases.The dam is raised and expanded on the basis of the first phase dam.According to the site conditions of the tailings dam, the research parameters are taken, and the 3D model of the dam break process of the tailings dam is established by using FLUENT software, and the migration distance, flow velocity and impact pressure of the tailings flow in 7 time periods within 10-100 s are studied and the influence on the stability of the second phase tailings dam, then according to the numerical simulation results to formulate the targeted prevention and control measures.The results indicated that as time goes on, the migration distance of tailings gradually increases, and the flow velocity and pressure first increase and then decrease.In the process of tailing discharge, the dam near the dam site is damaged most seriously, and the duration from the occurrence to the end of dam break is only 400 s.The impact force of tailings dam break is huge and rapid, but the numerical simulation results have guiding significance to the actual prevention and treatment engineering, and can effectively ensure the safety of tailings dam.