The Yangtze River Estuary serves as a critical water source for Shanghai"s urban development both currently and in the future. However, saltwater intrusion stands as the primary risk factor threatening the security of this water source, and developing resilient responses to this challenge is vital for the stable operation and high-quality development of the city. Firstly, focusing on the multiple key influencing factors of saltwater intrusion in the Yangtze River Estuary, this study systematically conducted an in-depth analysis of critical driving factors over decades before and after the Three Gorges Project. These factors include meteorological changes in the Yangtze River Basin and corresponding runoff responses, sea-level rise, changes in estuarine topography and geomorphology, local meteorological conditions and typhoon evolution in the Yangtze River Estuary, as well as human activity interventions. Subsequently, targeting four typical years (2006, 2011, 2014, and 2022) with prominent saltwater intrusion events, the study carried out focused research on the contribution and correlation of relevant influencing factors. Furthermore, a comparative study was conducted to analyze the differences and characteristics of saltwater impacts on the water intakes of Shanghai"s three major reservoirs (Chenhang, Qingcaosha, and Dongfengxisha) across the four typical years.Finally, in response to the new development trends of saltwater intrusion in the Yangtze River Estuary, the study explored response strategies and strategic research for water source security in estuarine cities. This paper holds certain reference value for ensuring the security of water sources in the Yangtze River Estuary and guiding the future strategic development of related fields.