Abstract: The engineering geological conditions of Lenggu hydropower station located in the middle reaches of Yalong River are very complex, and large-scale landslides are very developed. Taking Xiari landslide of Lenggu hydropower station on Yalong River as an example, the stability development trend of landslide after impoundment is studied by means of test and numerical simulation on the basis of detailed field investigation on the spot. According to the geomorphic morphology, material composition, drilling data and field investigation, the Xiari landslide is divided into three zones, among which the zone II has been deformed and damaged to some extent, and the stability is the worst. The numerical simulation shows that the overall stability of the landslide is fairly good before the impoundment, and the deformation only occurs at the front edge. After the impoundment, the deformation of the landslide is obviously enlarged and the front edge slides along the existing secondary slip zone. It is suggested that lattice anchor and anti-slide pile should be used at the front edge of the Xiari landslide, and the InSAR technology should also be used for early identification, monitoring and early warning of landslide hazards. This study provides an important basis for the prevention and control of reservoir bank landslide in Lenggu Hydropower Station, and has a certain reference significance for the study of the same type of landslide. This study provides an important basis for the prevention and control of reservoir bank landslide in Lenggu Hydropower Station, and has a certain reference significance for the study of the same type of landslide.