Abstract: Reservoir landslides are a common geological hazard in hydropower engineering construction. When landslides slide into the reservoir area, they may cause surges, river blockages, and even dam breaches, resulting in significant economic losses and casualties. Therefore, studying the deformation characteristics of reservoir landslides is crucial for efficient and timely identification and monitoring of early-stage landslides along the reservoir area. [Methods]In this paper, the Baihetan Reservoir area is taken as the study area. Based on Sentinel-1 radar images, broad-scale active landslide disaster identification and deformation information before and after the reservoir filling of landslides in the Baihetan Reservoir area are obtained using Stacking Interferometry Synthetic Aperture Radar (Stacking-InSAR) and Small Baseline Subset Interferometry Synthetic Aperture Radar (SBAS-InSAR) methods. Combined with Sentinel-2 images, Automated Water Extraction Index (AWEI) is used to extract reservoir water level data. One typical landslide with significant deformation of each type—ascending, descending, and pre-filling deformation—was selected to investigate the relationship between reservoir water level fluctuations, rainfall, and landslide deformation. [Results and Conclusion] The study concludes that: The method of extracting reservoir water level data using AWEI with Sentinel-2 imagery has shown good results in this study area. The average error between the extracted water level and the measured water level at the same time is 0.89 meters. This method has research value for areas lacking water level data.During the observation period, a total of 103 active landslides were detected in the Baihetan Reservoir area using both ascending and descending orbit images. Among these, 37 active landslides involved the front edge entering the water, and 23 landslides were deformed due to water level fluctuations. There is a strong correlation between reservoir bank landslide deformation and water level fluctuations, while the correlation with rainfall is weaker, and the decrease in water level has a greater impact on reservoir bank landslide deformation.