Abstract: The origin of Xiangshuikan rapids in the Dongting Lake is analyzed by using remote sensing geological and hydrodynamic methods. The effect factors of water steepfall in hydrology, geology and hydrodynamics, and the fluvial process upstream and downstream of the steepfall are discussed. It can be seen that the mutation of strata lithologic and sedimentation thickness, and the geologic structural unit distribution are the internal causes of the original bed falling-step formation. The precondition of the water fall is the original bed falling-step; the external conditions of the water fall are the lake boundaries and dynamic action of flow; and the combination of hydrological conditions decides whether the Xiangshuikan rapids obstructs navigation.