Shubeikeng No.1 reservoir(upstream of Xiaoxiyunlong river)and Shubeikeng No.2 reservoir(downstream of Xiaoxiyunlong river)are studied by applying hydraulic principle and GIS spatial analysis technology in the paper.Under the condition of excessive flood,it makes a comparative analysis of flood risks encountered by cascade reservoirs resulted from the downstream dam break and the downstream dam break generated by the upstream dam break.At the same time,measures for flood avoidance and transfer of affected residents are formulated.The comparative results show that when analyzing the reservoir inundation resulted from the excessive flood,it is not comprehensive to only consider the dam break flood analysis of a single reservoir in the downstream reservoir,and further consideration should be given to the downstream caused by the dam break of the upstream reservoir after exceeding the standard level of flood.The flood inundation analysis of the continuous collapse of the reservoir is of great significance to the safety of the lives and property of the people living in the downstream regions．