[Objective] This study proposes a dynamic flood risk assessment method for transmission lines in flood storage and retention areas by integrating multi-source satellite remote sensing. The aim is to enhance the disaster prevention and mitigation capabilities of power grids，as well as the efficiency of post-disaster emergency response. [Methods] The proposed framework consists of remote sensing monitoring of the flood process，inundation monitoring of transmission towers，and dynamic flood risk assessment. The method integrates Synthetic Aperture Radar （SAR） and optical satellite imagery. Specifically，the Sentinel-1 Dual-polarized Water Index （SDWI） and the Modified Normalized Difference Water Index （MNDWI），combined with Otsu’s thresholding algorithm，were employed to accurately extract flood extents. These were then fused temporally to reconstruct the flood evolution process. By incorporating the inundation dynamics of transmission towers，a risk assessment matrix centered on inundation duration and voltage level was constructed to achieve a dynamic quantitative evaluation. The method was validated through a case study of the catastrophic “23·7” Haihe River Basin flood in the Dongdian Flood Storage and Retention Area in 2023. [Results] The proposed method effectively characterizes the spatiotemporal patterns of flood risk for transmission lines within the study area： The assessment identified that 51.7% of the towers were at high risk，with this proportion reaching 92.2% for Ultra-High Voltage （UHV） lines. The dynamic evaluation revealed that risks escalate with the accumulation of inundation duration and converge towards downstream depressions. Overall，the risk distribution exhibited a strict dependence on voltage levels. High-risk zones were predominantly concentrated in core depressions with prolonged water stagnation，confirming that the ultimate pattern of flood risk is jointly determined by transmission line voltage levels and long-term inundation conditions. [Conclusion] From a methodological perspective，integrating SAR and optical imagery with targeted water extraction （SDWI-Otsu and MNDWI-Otsu） and temporal fusion strategies significantly improves the accuracy and continuity of flood extent extraction in complex scenarios，enabling dynamic reconstruction of the entire flood evolution process. The constructed two-dimensional risk matrix，based on inundation duration and voltage level，is physically interpretable with easily accessible parameters，allowing for rapid dynamic and comprehensive risk assessment. Future work will focus on improving the accuracy of tower inundation duration by incorporating space-air-ground integrated remote sensing and hydrological modeling. Additionally，more structural and environmental parameters，such as tower foundation types and soil conditions，will be integrated to build a more refined multi-dimensional risk assessment model.