Fluvial processes of mountain river in the Southeast Tibet have been severely modified by debrisflow dams. However,most of the researches on the debris-flow dammed lake focus on the ancient dammed lake associated with the research on the long-time scale climate change. Researches on the detail fluvial process of debris-flow dammed lake from the short-time scale perspective are insufficient. In this study,we detailed the methodology to extract the sedimentation rate,and the effect of the debris-flow dammed lake on the bed structure is calculated.