Abstract: The southeast of the Qinghai-Tibet Plateau in China, contains the richest hydro-energy resource. There is an urgent need for identification and monitoring of the large number of landslides developing in Xiluodu reservoir area. This article makes it possible to observe the deformation of a large landslide before and after impoundment using archived ALOS PALSAR,ENVISAT ASAR and recent programmed TerraSAR-X synthetic aperture radar data based on InSAR Technology. Based on the geological background and field investigation, the deformation characteristics and sliding mode of the landslide are revealed. (1)The landslide is an ancient landslide, and the deformation area today is in front of the accumulation body. It had obvious deformation before the impoundment, and the maximum deformation is located in the middle of the sliding body with main line- of -slope deformation. The rear area of the landslide is a material reduction area, with main vertical deformation. According to the interference phase of the ascending and descending data, the sliding mode is considered as a push type. (2)D-InSAR results show that the slope develops three value ladders after the impoundment, where has cracks and raised paths through fields, and the sliding mode is a pull type. (3)The groundwater activity is strong in the study area, and the field survey shows that the underground water level is high. The sliding surface has been connected before the filling. Due to the rising reservoir water level, saturated rock mass in the central area of the landslide and moist surface structure, which decrease the anti-sliding ability, and the landslide sliding mode change from the push-type to the pull-type.