Based on the one- and two-dimensional coupled hydrodynamic model of middle and lower reaches of the Yangtze River, taking 1954 and 1998 flood as the typical floods, the flood processes of the Lake Dongting area before and after the flood control operation of the Three Gorges Reservoir were simulated. Quantitative analysis was carried out for the flood control contribution of the Three Georges Reservoir for the Lake Dongting area. The results indicate that, during the basin-wide severe flood period of the Yangtze River such as 1954 and 1998 floods, after the operation of the Three Gorges reservoir, the flood control pressure of the three rivers in southern of Jingjiang River and the Lake Dongting area was effectively alleviated. About 1.58% and 0.61% of the flood diversion volume and 24.6% and 18.4% of the peak discharge of the three rivers in southern of Jingjiang River could be reduced; in addition, 0.50-0.93 and 0.51-0.82 m of the maximum water level of the Lake Dongting area could be reduced. From the perspective of spatial distribution, the decrease value shows a pattern that the north and east was stronger than the south and west. Under the extreme floods the Yangtze River such as 1954 flood, the flood volume in the Lake Dongting area could be decreased by 4.32 billion m³ after the Three Gorges Reservoir operation, whereas excessive floods still should be handled properly.