Abstract: Overtopping failure of concrete-faced rockfill dams involves a complex water-soil-structure coupling mechanism. Based on water-sand dynamics theory, slope stability analysis methods, and principles of material mechanics, this study examines the development process of longitudinal and cross-sectional failure of the dam body during overtopping failure of concrete-faced rockfill dams, and reveals the evolution mechanism of failure morphology and flood flow. In general, the failure of the face dam is a coupled process involving continuous erosion of dam material, intermittent instability of the damaged slope, and multiple fractures of the suspended face. In the longitudinal direction, the development of the breach mainly exhibits the cyclic coupling process of continuous erosion of the rockfill and failure of the downstream dam slope panel. In the cross-sectional direction, the collapse is primarily reflected in the evolution of the rockfill collapse form, which is influenced by traceable erosion, lateral encroachment denudation, and instability collapse of the slope. The intermittent fracture of the suspended panel, caused by the continuous expansion of downstream dam slope failure, leads to the multi-peak characteristics of the failure flow curve, with the peak values serving as important indicators for assessing the primary and secondary degrees of failure. The research results provide an experimental basis for establishing a dam failure process prediction model and conducting disaster risk assessments.