Abstract: Centrifugal model tests on dam break due to overtopping are carried out based on the gradation curves of Tangjiashan barrier dam by establishing the correspording physical models, and a method for calculating the rectangular weir flow in the centrifugal field is derived. The overtopping process and mechanism of barrier dam is analyzed deeply, and the failure mechanism is verified by the curve of breach flow and the development of breach top width taken from model tests. The test result show that the breach of barrier dam develops throughout during the whole process of overtopping along the width direction. The development of barrier dam breach along the depth direction, however, stops at earlier time due to the accumulation of large particles in the downstream slope, and coarsening phenomenon in the downstream slope can be observed obviously at the later stage of overtopping. Thus, the bottom part of barrier dam will survive after dam break, and the condition of whole collapse has few cases. In addition, the size of breach remaining will be less than that of the homogeneous earth dam under the same condition.