Abstract: To address the weak resistance of earth-rock dams against overtopping flow under extreme flooding, this study established a hydrodynamic model for dam overtopping using the FLOW-3D platform. The numerical simulation of solid-liquid two-phase flow during dam breaching was conducted based on the standard RNG κ-ε turbulence model and the Volume of Fluid (VOF) method, considering varying structural characteristics and dynamic disaster conditions. The results show that: ① During overtopping, the breach initiation time and total breaching duration increase exponentially with the dam crest width. When the crest width reaches 8 m, the delay growth rate approaches 1;② As the upstream slope becomes gentler, the breach formation time first decreases and then increases, reaching a minimum at a slope ratio of 1:2. In contrast, the total overtopping failure duration is negatively correlated with the slope ratio, showing a stable prolongation of nearly 20 s; ③ For dams of different heights, when the dam height increases to 15 m, both the breach initiation time and erosion duration exhibit an upward trend, peaking at 15 m. Beyond this height, the breaching duration first decreases, then increases, and finally stabilizes, while the breach formation time continuously advances, reducing by nearly 90 s per 5 m height increase; ④ With increasing inflow discharge, the overtopping breaching duration is significantly shortened, accompanied by intensified lateral and vertical erosion, continuous breach widening, and an earlier occurrence of peak cross-sectional flow.