Since mountain flood disasters involve many disciplines such as meteorology,hydrology,hydraulics and dynamics,the research on the evolution mechanism is not comprehensive enough.In order to study the evolution mechanism of mountain flood disasters,taking Maogongdong small watershed as an example,using FLOW 3D software to carry out three-dimensional numerical simulation,a three-dimensional numerical model of the solid terrain within a range of 300 meters on both sides of the river was established,and the dynamic process of mountain torrent disasters was simulated and calculated.On this basis，the inundation mechanism of mountain flood disasters is analyzed,and the results have certain reference significance for subsequent analysis of the mechanism and evolution of mountain torrent disasters.