Abstract: The Jiala barrier lake threatens the population,urban facilities,and ecological environment. It is in an uninhabited area and thus difficult to investigate and study its formation mechanism. In March 2019,we conducted a barrier lake site investigation. The topography,lithology of the remaining dammed body,and the surge damage phenomenon were investigated,combined with the grain size and material composition of the dammed body to reveal the formation process and damage mechanism. The results showed that the deposits of Sedongpu gully on the left bank of Yarlung Zangbo River rushed into the river channel three times and formed the barrier lake. The breach took place twice on October 19 and 31,2018, with the breach discharge of 32000m³ ·s^-1 and 19000m³ ·s^-1 respectively. The barrier body volume caused by the first two activities reaches 65 million m³,with the height of 85m. And when the breach occurred,the lake water storage reached 600 million m³. The barrier body volume induced by the third activity is about 10 million m³ with the height of 67m. When water storage was 326 million m³,the second breach occurred. It reveals that the dammed body derived from accumulated moraine which has high water content and ice blocks,suggesting a unique failure mechanism and flood characteristics like debris flow accumulation. The damming events in the Yarlung Zangbo River occurred frequently. This study can provide a reference for the disaster response of the barrier lake in this region.