Based on the theory of flow diversion ratio in bifurcated rivers, integrating the classical slice velocity analysis methods such as the inclined slice method and the influence of water resistance, a calculation method for the far-field surge propagation in a bifurcated river was proposed. Taking the Mogu toppling landslide of the Lianghekou hydropower station in the Yalong River as an example, considering the working condition of the Mogu toppling landslide to the bifurcated river in front of the dam of the Lianghekou hydropower station, the generation and propagation characteristics of the toppling landslide surge were analyzed by the proposed method. The initial surge height, dam front surge height and dam climbing height of two typical landslide sliding modes were obtained under the condition of the second phase storage water level of 2785 m. The results show that the surge height of landslide surge is 9. 32 m in front of the dam when the landslide slips along the fracture zone. When sliding along the strong and weak toppling interface, the surge height of the landslide surge is 14.73 m in front of the dam.