Abstract: The safety risk of overhead tailings pond is huge， and it is easy to cause major safety accidents. Therefore， it is of great significance to study the evolution process and downstream protection measures of debris flow in overhead tailings pond. Aiming at the tailing pond with open plain terrain in the downstream， through two methods of model test and numerical simulation， the sediment deposition thickness and inundation range of each position in the downstream of the dam body under different layout forms of the downstream retaining dam are studied. On this basis， the layout forms of the downstream protective retaining dam are optimized. Based on the analysis of the downstream sediment deposition thickness and inundation range after dam break， it can be concluded that:① the retaining dam has the dual function of retaining and diversion， and the diversion is divided into transverse diversion and longitudinal diversion. ② the function of the retaining dam is different with different dam body angles: the larger the angle between the dam body is， the more obvious the retaining function is； the smaller the angle between the dam body is， the more obvious the diversion function is. ③ The retaining dam with an included angle of 128° is the best protective measure ， because the angle of the dam type can slow down the impact force of the discharged sediment on the dam body， and the two-way diversion of the dam type increases the flow range of the discharged sediment， reduces the thickness of the downstream sediment deposition， enables the sediment to be effectively discharged around， and reduces the harm to the downstream residents. The research results can provide decision-making basis for the optimization of downstream protective measures of tailings pond.

Key words: overhead tailings pond, blocking dam, model test, numerical simulation, thickness of sediment deposition, submerged area