Abstract: By means of the centrifugal model test system for break of dams, experimental studies on the break of a homogenous earth-rock dam with three different heights (the largest one is up to 32.0 m) and a clay core dam of 16.0 m in height due to overtopping failure are performed. The break mechanism and the development rules of breaches are clearly released. It is found that for the homogeneous earth-rock dams, with the increase of dam height, the longitudinal down cutting of the breaches together with the collapse rate of breaking slopes obviously increases, and the hydrographs of break discharge become steeper. The peak discharge increases and emerges earlier, and the duration of dam break becomes shorter. For the clay core dams, the break mechanism and the breach development rules are obviously different from those of the homogenous dams. With the increasing erosion of downstream dam shells by overtopping flows, shear failure of the clay core occurs and the discharge through the breach abruptly increases. Based on the above test results, numerical models for depicting the break development of homogenous earth-rock dams and clay core dams and for calculating the hydrographs of their break discharges are proposed. The methods for the relevant numerical models are also put forward. The rationality of the proposed numerical model is validated through comparison between the numerical simulations and the observed results.