Abstract: Considering the wide gradation characteristics of barrier dam materials, an additional force perpendicular to the water flow direction is introduced into the model to consider the block function and bridging effect of coarse particles on fine particles, and the way in which fine particles surround and fill coarse particles. A numerical model with a calculation method describing the discharge process and breach development due to overtopping failure of a barrier dam is proposed. The model and the calculation method have been used to calculate and analyze the discharge process of Tangjiashan barrier dam. The calculated results are close to the observed data, which indicates that the model and the calculation method are reasonable. A comparative analysis on the influences of the discharge process of the Tangjiashan barrier dam with different cross sections of a drainage channel is carried out, and it is found that the depth and the cross section of the drainage channel have a major impact on the discharge process. With the increase in drainage channel depth, the discharge efficiency is improved significantly, but the risk of the downstream would be higher. For the trapezoid drainage channels with the same depth, if the cross section is changed to compound section by decreasing the bottom width, the excavation work decreases without causing a considerable decrease in the discharge efficiency. In addition, the discharge curve is flatter, indicating a lower peak discharge and a longer time to reach peak discharge, and therefore it will diminish a risk for the downstream of the dammed lake.