Abstract: Debris slopes represent a typical geohazard feature on the Qinghai-Tibet Plateau, where their stability critically affects the safety of transportation infrastructure. This study investigates the failure mechanism and evolutionary behavior of interbedded debris slopes under slope-cutting disturbances, aiming to provide theoretical support for disaster prevention in such regions. A typical interbedded debris slope in the Dequ River Basin of the Qinghai-Tibet Plateau was selected as the research object. Through a combination of theoretical analysis and MatDEM-based discrete element numerical simulation, the entire process of deformation and failure triggered by slope cutting was systematically examined. The results indicate that the failure mode of the interbedded debris slope after cutting is typically progressive. The underlying cause lies in the significant differences in mechanical properties between the uncemented and cemented layers exposed on the slope face. This progressive failure exhibits spatial staging, temporal periodicity, and localized recurrence. The failure process can be divided into five stages: slope-cutting disturbance, cavity formation, crack development in the cantilever section, collapse and disintegration, and cycle restart. Based on theoretical derivation, a criterion for identifying progressive failure in interbedded debris slopes after cutting was established, quantitatively expressed using the maximum cantilever length(l_max)of the cemented layer. This study identifies the typical"uncemented-cemented" interbedded structure in debris slopes, clarifies the mechanism and evolution of progressive failure, and proposes a theoretical criterion for failure identification. The findings offer a scientific basis for disaster prevention and safety management along major transportation routes in debris slope-prone areas of the Qinghai-Tibet Plateau.