Abstract: On October 17, 2018, a massive ice avalanche-debris flow occurred in the Sedongpu Basin on the left bank of the Yarlung Zangbo River in Tibet. The sliding mass scoured the glacial deposits and loose deposits in the gully bed and then transformed into a debris flow. Eventually, a barrier dam was formed and blocked the Yarlung Zangbo River, which seriously affected the safety of residents and social and economic development. In this paper, a three-dimensional numerical simulation of this event was performed based on remote sensing. A dynamic analysis (DAN^3D) model was utilized to analyze the dynamic characteristics of sliding mass, and the Frictional-Voellmy composite model was selected to reproduce debris flow accumulation characteristics, movement speed, and scraping depth. The simulation results are consistent with the actual survey results and have good reliability. Based on field investigation, the electrical resistivity tomography method was used to reveal the post-event accumulation characteristics of the ice avalanche-debris flow in Sedongpu gully. The results showed that DAN^3D could well simulate the accumulation shape and maximum thickness of sliding mass, which verified the effectiveness of DAN^3D simulation. The results of the study can help forecast similar events and provide new research ideas for the mechanism research of such disasters for future prevention and control projects.