Eastern Himalayan Syntaxis (EHS) is a tectonically active region that undergoes continuous geomorphic changes.Large landslides are predominant in this region.A giant landslide called Jiaobunong landslide on the northwestern flank of the EHS were studied and simulated to investigate the formation mechanism,evolutionary process,and failure mechanism of the landside,so that we could better understand the large complex ancient landslides in this region.Field investigation,geological background analyses,and numerical modeling were conducted to reveal the natural and seismic characteristics,as well as dynamic process of the landslide.The results show that the Jiaobunong landslide was the result of long-term geological and geomorphic evolution.Uplift,river incision,weathering,fault creep,glaciation,and earthquakes play key roles in the formation of landslides.Given the huge landslide volume,strong seismicity of the study area,proximity to an active fault,and the need for extra forces to induce landsliding,the Jiaobunong landslide was triggered by a paleo-earthquake.Using numerical simulation based on the discrete element method,the slope dynamic response of the earthquake as well as the mass movement and accumulation process was reproduced.Simulation results showed that the landslide movement experienced four stages:initiation phase (0-5 s),acceleration phase (5-35 s),deceleration phase (35-95 s),and the compaction and self-stabilization stage(after 95 s).The rock mass was disintegrated and experienced strong collisions during the movement.The dammed lake gradually disappeared because of long-term river incision by the overtopping river water.These processes play a vital role in the evolution of landforms in the region of EHS.