The debris flow dam is a common type of barrier dams, which shows significant differences from other types of barrier dam such as landslide dam, moraine dam in their formation processes, dam body shapes, and internal compositions. The basic breaching parameters such as flood peak discharge are vital indicators of risk assessment. In this study, we elucidated the failure process of the debris flow dam through the flume experiment, and built the calculation equation of the breaching parameters by selecting critical factors. The result shows that the overtopping failure process of the debris flow dam is capable of forming significantly retrogressive scarps, and the failure process experiences three stages, the formation of the retrogressive scarp, the erosion of the retrogressive scarp, and the decline of the retrogressive scarp. Five factors used for establishing the calculation equations for peak discharge (QP), final width (Wb) of the breach, and duration (T) of the debris flow dam failure are dam height (h), reservoir capacity (V), the fine grain content (P0.075) of the soil, the nonuniformity coefficient (Cu) of the soil, and the upper limit grain size (D90) of the soil, respectively. In the three equations, the correlation coefficients between Qp, Wb, T and the five factors were 0.86, 0.70, 0.63, respectively. The equations still need to be modified and verified in actual cases.