Lake Dongting has been subjected to drought which threatens grain production and people's lives. For investigation of extreme droughts in 2006 and 2011, water surface changes and its tempo-spatial variation characteristics were identified with data of remote sensing images. The similarities and differences for the two drought events were analyzed from respects of changes in temperature, precipitation, runoff and storage capacity, by using the hydrological and meteorological data. The main results are as follows. The first drought lasted from July to December in 2006. The water area expanded from the lake center to all-around low lands. The peaks occurred at July and receded at August in 2006, where the reduced area focused on periphery of east Lake Dongting and north of south Lake Dongting. Drought was mainly caused by discharge reduction in 2006. While in 2011, drought lasted from April to November, and was aggravated in September. The inundated area increased sharply in June and retained a high level until August. During water rose period, water submerges from the center to the surrounding areas, while in water withdrawal period, change direction of water area reverse of water rose period. Drought was caused by combined effects of hydrological and meteorological factors in 2011. The results revealed that there were diversity and complexity of drought causes in Lake Dongting, which can provide useful guidance and advice for making scientific measures to abate drought disaster.