The evolution of the longitudinal process of tailings dams breaching during overtopping failure was systematically analyzed by three sets of flume breaching tests at different flow rates, and the relationship between erosion rate and shear stress was discussed.The results show that the tailings dam overtopping failure shows a longitudinal pattern of steep canyon erosion with a pivot point rotational erosion pattern.The outburst flow and density both show an upward and then downward trend, but with large fluctuations in water-sand flow density. Different inflow flows affect the erosion rate of the dam at each stage, with the least effect on the erosion rate in the first stage and the greatest effect in the second stage. The maximum erosion rate increases with the increasing upstream inflow, but does not affect the relative change of the erosion rate along the dam bed.The erosion resistance of the soil on the dam is not only recated to the strength of the dam material, but also closely related to the density of the fluid on it.