Abstract: Based on the dam breach case data of Sheyuegou Reservoir in Xinjiang Autonomous Region of China, the model tests on overtopping-induced breach of asphalt concrete core dams are conducted in the flume erosion model test system, and the process of erosion of dam shell materials and bending of core walls is visually demonstrated. It is found that the asphalt concrete core with strong erosion resistance has important influences on dam breach process. The breach process of asphalt concrete core dams due to overtopping can be divided into three stages: retrogressive erosion of dam shell materials, the first fracture of asphalt concrete core until the occurrence of the peak flows, occurrence of multiple fractures of core wall until the stabilization of the breach morphology. Based on the breach model test results, a mathematical model is developed to simulate the breach flow discharge and the breach morphology evolution of asphalt concrete core dams due to overtopping. The highlights of the model are the simulation of the exposed length of asphalt concrete core by soil erosion formula, and the calculation of breaking time, breaking length, and number of breaking time of the exposed core wall by the moment balance method. Therefore, the coupling mechanism between dam shell materials and core wall of asphalt concrete core dams can be reflected reasonably during dam breaching. The mathematical model is used to conduct back analysis of the dam breach process of Sheyuegou Reservoir, and the calculated results show that the relative errors of important breaching parameters are within ±25%, which gives a good perfomance in dam breach modeling. The research results can provide reference for simulation of breach process of overtopping-induced asphalt concrete core dams.