A hydropower station is to be constructed on the Yalong River. Pan Jiazheng slice method is used to calculate the speed of possible landslides in the unstable slopes in the reservoir. But the height of their surges is worked out using Empirical formula method by IWHR and Pan Jiazheng method as well. Based on the two results, the surge height is acquired as 0.41~0.88 m by the future dam which exerts little effect on the project to be built. This calculation-analysis method serves as a reference for similar projects.