Using field data from the 1950抯 to 1990s, the flood storage capacity of Dongting Lake was analyzed. The impacts of sediment deposition in Dongting Lake and in the reach of the Yangtze River from Chenglingji to Hankou were analyzed. The effects of land reclamation in the lake region on the flood storage capacity also were analyzed on annual and other time scales. The study shows that sediment deposition in the downstream reach is the main reason of flood storage increases under the same inflow condition. The field of water storage from Dongting Lake was analyzed. The impacts of sediment deposition in Dongting Lake and in the reach of the Yangtze River from Chenglingji to Hankou were analyzed. The effects of land reclamation in the lake region on the flood storage capacity were were analyzed on annual and other time scales. The study shows that sediment deposition in the downstream reach is the main reason of flood storage increases under the same inflow condition.