With the completion and operation of the Longyangxia Hydropower Station, the infiltration and erosion caused by water level fluctuations on the reservoir bank slope led to the collapse of both banks of the reservoir area, which affected the stability of the landslide. SBAS-InSAR(small baseline subset interferometic synthetic aperture radar) technology was used to identify and monitor the landslide in the Longyangxia Reservoir Area by using the Sentinel-1A data of ascending and lowering rails, and the influence of water level fluctuation on landslide deformation was studied. The results show these as follows. A total of 15 unstable slopes were identified by InSAR technology for deformation monitoring in the Longyangxia Reservoir Area, of which 6 were known landslides with a deformation rate of -80~30 mm/year. The ATL13 water data of ICESat-2 satellite was used to extract the water level of Longyangxia reservoir area. Taking the Mangla estuary landslide and Longxi landslide as examples, the correlation coefficient between the deformation of the landslide and the water level in the reservoir area was quantitatively calculated by using the Spearman correlation coefficient, and the results show that the average correlation coefficient of the two landslides is greater than 0.6, and the correlation coefficient is the largest when the water level drops, and the maximum value is 1.0. In the Mangla estuary landslide, the maximum correlation coefficient is 0.844 when the landslide deformation lags behind the water level in the reservoir area for 2 months, and the maximum correlation coefficient is 0.841 when the landslide deformation lags behind the water level in the reservoir area for 4 months in the Longxi landslide. Wavelet analysis was carried out to analyze the periodic deformation of typical landslide deformation time series and the water level in the reservoir area by singular spectrum analysis, and it was found that the correlation between the two was significant, and there was a lag period of about 2 months and 4 months between the landslide deformation and the water level in the reservoir area of the Mangla Estuary landslide and Longxi Landslide, respectively. The result revealed that fluctuations in the water level of the Longyangxia Reservoir (especially water level drops)are key factors affecting the stability of reservoir bank landslides, clarifying the delayed characteristics of deformation response and providing important scientific evidence for landslide risk warning and prevention in the reservoir area.