Abstract: At present, cascade reservoir dams become increasingly important, but the research is still relatively inadequate at home and abroad. This study relates the upstream and downstream reservoirs using flood regulation and develops a numerical model for a sequential dam break of earth-rock dams based on the dam-break model DB-IWHR. In a case study of the Tangjiashan-Jia cascade reservoirs, simulation and risk analysis are made under the conditions of different discharge capacities and different early warnings for the downstream reservoir. Results show that for Tangjiashan reservoir, the calculated flow rates of its dam break floods are a little larger than the measured results but they agree quite well. In cascade reservoir cases, the risk of sequential dam breaks can be significant cut down through enhancing early warning for reducing reservoir storage in advance or increasing the discharge capacity of downstream reservoirs.