After the normal operation of the Qiaoqi reservoir in 2007, about 40 landslides have been triggered by the influence of reservoir levels and precipitation, that caused a serious threat to socio-economic activities. Taking the Kadui-2 landslide as a case study, three-year (2015-2017) GPS monitoring network was implemented to observe surface deformation. Based on the reservoir level fluctuation and precipitation, coupled seepage-stability simulations were conducted using Geo-studio to obtain distribution behavior of saturation lines and stability. The slide mass experienced persistent deformation with a maximum cumulative displacement of 331.34 cm. The long-term displacement data shows a step-like characteristic and follows an acceleration phase from December to April during reservoir draw-down periods and subsequent low strain rate from May to November during reservoir-filling operation. The simulation results reveal that the landslide stability lag behind the reservoir level and maximum internal hydraulic forces are operating within the saturation zone. The landslide stability and displacement rate is dominantly controlled by the change of reservoir level only and rainfall has no significant effect. Furthermore, the total collapsed area increased significantly by 18 % from 2012 to 2014 at the head of landslide that shows a retrogressive type movement.