Dam break usually causes huge disaster.Especially in considering dam safety emergency response,dam break flood prediction research is particularly important.In order to research the impact of dam break flood,taking Gaoping Reservoir in Renhua County,Shaoguan City as an example,this paper constructs a hydrodynamic model of reservoir dam break based on HEC-RAS software,simulates the working condition calculation of dam break due to overburden under these conditions that the reservoir encounters the check flood once in a thousand years and the spillway gate could not be opened,and analyzes the downstream submerged depth and submerged area after the dam break.It puts forward technical scheme of reservoir dam break flood analysis based on HEC-RAS software for reference of the technical personnel,which can be applied to the disaster prevention and reduction work of reservoir to quickly analyze and calculate the dam break submerged area of reservoir.