Abstract: Excessive rainfall has led to frequent incidents of check dam breaches, and there is an urgent need to conduct rapid dynamic evaluation research on check dam breach disasters on the Loess Plateau. Taking the process of rainfall induced dam breach as the research core, a "rain flood sand breach" disaster evaluation method is constructed, and the coupling effect of "soil water sand" is integrated throughout the entire process of dam breach, establishing a mathematical model of water sand dynamic dam breach for check dams. Taking the "7.15" rainfall in the Wangmaogou watershed in 2012 as an example, rapid determination of the failure status of check dams, research on the impact of sudden changes in sediment supply, and rapid positioning of dangerous dam bodies were carried out to achieve rapid dynamic evaluation of dam failure disasters. The results indicate that the use of the water sediment dynamics dam breach mathematical model to determine the dam breaches of Huangbaigou 1 # dam, Kanghegou 1 # dam, and Kanghegou 2 # dam is consistent with the actual breach situation; Considering the impact of rainfall induced runoff surges and sudden changes in sediment recharge on the evaluation of dam failure disasters, the peak flood times of Huangbaigou 1 # Dam, Kanghegou 1 # Dam, and Kanghegou 2 # Dam were advanced by 24 minutes, 21 minutes, and 26 minutes, respectively. The peak flow rates increased by 4.24%, 1.53%, and 4.76%, respectively. The peak flood times were advanced and the peak flow rates were higher, resulting in safer results and helping to issue early warnings; With the increase of rainfall, the number of dam failures determined by ignoring sediment action is smaller than that determined by considering sediment action, and sediment action cannot be ignored.