Based on measured data of the dam breach of Tangjiashan Barrier Lake, the process of the dam breach was analyzed using the BREACH model and the DB-IWHR model developed by the China Institute of Water Resources and Hydropower Research. A sensitivity analysis of the two models to different parameters was also performed. Results show that, using the parameters of the dam, the two models can both reflect the flooding process induced by the dam breach; the calculated results of the peak flow are more sensitive to the input parameters of the downstream slope and porosity in the BREACH model; the DB-IWHR model improves the calculation of the erosion parameter and downstream water depth, resulting in calculated results less sensitive to the input parameters; and the DB-IWHR model provides software in the Excel format, with a high stability in numerical analysis, which is transparent, self-explanatory, and friendly to practitioners.