Abstract: Barrier dams, formed by the rapid accumulation of unstable geological materials that block river channels, often pose severe risks to downstream life and property in the event of failure. Using the Baige "11·3" barrier dam as a prototype, the overtopping breaching process was investigated through flume model tests, considering the influences of water storage capacity, fine particle content, and geometric scale. The results indicated that the overtopping breaching process can be categorized into three main stages: headward erosion (Stage Ⅰ), progressive failure (Stage Ⅱ), and stabilization (Stage Ⅲ). Increasing the water storage capacity from 3 200 liter to 4 200 liter and 5 400 liter raised the peak flood discharge by 20.1% and 39.5%, respectively, while also deepening and widening the breach channel. A lower fine particle content may lead to seepage within the dam body during the water storage phase. As the fine particle content increases, the erosion resistance and stability of the dam decrease, resulting in an earlier occurrence of the flood peak, an increase in peak discharge, and a wider and deeper breach channel. Additionally, the geometric scale of the model should not be too small. For a model dam with a height of 10 cm compared to one of 32 cm, the peak breach discharge increased by 45%, the breach channel widened by 23%, and the residual dam width decreased more significantly. The findings provide a valuable reference for analyzing the failure mechanisms of barrier dams and for designing flume model tests.