Abstract: The wetlands of Poyang Lake and Dongting Lake, both of which were naturally connected to Yangtze River, are of irreplaceable natural and cultural significance. In  recent years, especially after the operation of the Three Gorges Dam (TGD), wetland landscape patterns of the two lakes have changed, which has significant impacts on the  regional ecological balance and social economic development. Based on the datasets derived from Landsat 7, we quantitatively assessed the changes of the wetland patterns before  and after the operation of TGD and identified the differences between the two lakes, by employing the Decision Tree Classification and Gauss Regression method. This study aims  to better understand the ecological effects of large water conservancy project and to provide a scientific basis for wetland protection and reconstruction. The results suggested  that there was barely change of the Dongting Lake water level during the dry period between 2000 and 2014. The historical evolution patterns of Dongting Lake wetland indicated  that although a small part of vegetation occupied the region of mudflat and water body, there was little change in area of these three typical wetland landscape types. By  contrast, the lake level of Poyang during the dry period dropped significantly after the operation of TGD. Moreover, the water body has shrunk by nearly 14% and vegetation coverage has increased by around 8%. Compared with the situation in 2000, the evaluation of vegetation distributed in the wetland of Poyang Lake in 2014 has decreased more than  1 m. The different evolution patterns in the wetlands of the two lakes were mainly attributed to the different extents of drought stresses.