Abstract: In view of the complex dam break process caused by heavy rain and floods,rapid changes in dam break flow and breach,large disaster hazards,this paper takes the actual dam break flood of Sheyuegou Reservoir as the research object by using measured and survey data.This paper simulates and analyzes Sheyuegou Reservoir flood formation,dam break process,dam break flow and mechanism based on a spatio-temporal variable source hydrological model and two-dimensional hydrodynamic method. The results of the study show that the simulated value of peak discharge is 1 915 m3/s,and the error is only 3.5% compared with the survey results. The extreme heavy rainfall in a short duration caused the flood that far exceeded the flood control capacity of the reservoir,which caused the dam to burst. The second and third teams of Ergong Village were affected most seriously,and the submerged water depth was between 2～6 m. Two flood peaks in the downstream river course and the narrowing of the downstream river course of the dam are important reasons,which cause economic and property losses in the downstream villages. The method adopted in this paper can better solve the calculation problems of the storm flood,dam break process and flood inundation process in Sheyuegou Basin. It can provide support and technical reference for dam break mechanism analysis and disaster loss assessment.