Lake has an important role of Earth’s hydrologic cycle. The changing of lake water area shows the ecological health of lakes by instant feedback. Most analyses of long-term monitoring of lake area are not comprehensive enough, This study based on the remote sensing images from 1977 to 2021, combined with the Keyhole satellite data, hydrographic survey, meteorology monitoring and land use change survey, investigated the Poyang lake water area changes. Moreover, examined the response relationship between lake water area and the impact factor, analyzed the influence of river lake interaction on lake water area.The results showed that: (1) From 1977 to 2017, the water area of Poyang Lake in flood season (June to September) and dry season (November to Next February) showed a significant downward trend by years. (2) In flood season, runoff, sediment, precipitation has significant correlation with water area. In dry season, sediment showed a significant correlation with water area. (3) The Three Gorges Dam water impoundment at the upper reaches of the Yangtze River weakened eliminated the blocking or reversing flow from the Yangtze River, caused the water area decreased in advance at the end of flood season after 2005, and decreased rapidly in dry season after 2003. (4) The change of lakebed elevation caused by sedimentation and human activities also accelerated the shrinkage of water area. Result demonstrated that the variation of river lake interaction is the primary cause of Poyang Lake water area dramatic change.