Abstract: As a production of natural process, the landslide dam has poor structural stability, and most of which will finally fail due to overtopping, which will pose tremendous risks to the people and property in the inundated area. Therefore, it is of significant importance to predict the discharge hydrograph for the breach process of landslide dams so as to provide theoretical and technique supports to the dam emergency plan for dam breaching. In this study, based on the geometrical characteristics, physical and mechanical properties of a landslide dam, a numerical model for the breach process of the landslide dam due to overtopping failure is developed. This model can reasonably reflect the evolution and discharge hydrograph of the breach under the hydrodynamic condition. Meanwhile, the dam breach case of Yigong landslide dam is chosen as the representative to testify the proposed model. The comparison of the measured and calculated results shows that, the relative errors for the peak discharge, final breach widths, and time to peak are within ±15%; furthermore, the breach discharge hydrograph is in accordance with the measured one. Thus, the rationality of the model is verified effectively. The sensitivity studies show that the dam breach process is sensitive to the residual dam height, the erosion mode (one- or two- sided breach), and the soil erodibility.