Poyang Lake is the largest freshwater in China. Continual monitoring on its hydrologic changes can supply basic data for ecological environment researches and is favorable for studying the exchange between the Poyang Lake and the Yangtze River or other rivers in the watershed. Hydrologic changes of Poyang Lake are essential to land-surface process studies and water resources management. Altimeter data and high-frequency MODIS images were used in this paper to obtain water levels, inundation extents and lake storage changes of Poyang Lake during 2000-2015. Then water exchange between Poyang Lake and Yangtze River was estimated based on water balance equation. The results showed that lake inundation presented a large fluctuation and an obvious seasonality. The maximum area was 3600 km ², approximately 7.5 times of the minimum (482 km ²). Areas in the years 2004, 2007, 2009 and 2011 were smaller and the situation improved after 2012. The extent shrunk to less than 500 km ² in dry season (January, February and December) when water level at Hukou Station was only 4.71 m. At that time, the water surface inclined from south to north, and the water level difference between south and north could reach 2.59 m. The increase of lake storage in dry season was 3 km ³ relative to the minimum during the study period. Surface extent was usually greater than 2670 km ² in wet season (June-September) when water level was higher than 15 m and the surface was almost flat. The increase of lake storage in wet season was 12 km ³ relative to the minimum during 2000-2015. Water exchange between Poyang Lake and Yangtze River was from 7 km ³ to 40.66 km ³ during the research period and water from the lake to the river occurred in 93.33% time of the year. The flow water volume had obvious seasonality. Usually, the exchanged volume in May and June was more than that of July and August when precipitation increased in the upper-middle reaches of Yangtze River, thus more volume of the main stream and water was hindered to flow from Poyang Lake to Yangtze River.