Abstract: This paper takes a tailing pond as the prototype for modeling the effect of flood overtopping and dam break under different deposit compactness. Model similarity theory is adopted for the experimental researches under loose state, dense state, and solid state respectively with different compactness and densities to study the process and mechanism of tailings pond outburst by flood overtopping. Our results suggest that the general process of overtopping dam failure can be divided into three stages: the forming stage of fine gullies, the stage of trace erosion which leads to the vertical development of breaches, and the horizontal development stage of collapse. By analyzing the schedule of the key failure points of the three kinds of dam failure with different compactness, it is found that increasing the compactness of the deposits may effectively delay the formation time of debris flow in dam break. The modeling results are helpful for evacuation of downstream residents and making of corresponding rescue plans.