Abstract: Emergency disposal of water in earthquake-induced dammed lakes must adequately utilize fundamental data for efficient decision making. This paper presents a comparative study of the rapid estimation of downstream flood risks induced by dammed lakes using the Muskingum and Hydrodynamics methods combined with remote sensing，DEM，hydrologic data，and UIS techniques. Both methods were used to calculate the downstream potential impact area from the Tangjiashan dammed lake when the dam-break water level reached 690m. The results from both methods showed that the downstream Beichuan Town would be submerged.The rapidity，accuracy，and complementarities of both methods were evaluated based on the the potential impact area results，data requirements，and calculation times.