Abstract: As the second biggest freshwater lake, Dongting Lake plays an important role in floodwater adjustment of and water supply for industry, agriculture and life in the middle and lower reaches of the Yangtze River. The serious eutrophication was presented by the inorganic nitrogen in previous studies for the Dongting Lake. However, the organic nitrogen forms and release were still not clear until now. In order to reveal the spatial distribution and the release risk of nitrogen in lake sediments, nitrogen species, including exchangeable nitrogen (EN), hydrolysable nitrogen (HN) and nonhydrolysable nitrogen (NHN) in surface sediments of Dongting Lake were studied by sequential extraction methods. Concentration and release flux of bioavailable nitrogen (BN) were further measured to evaluate the contributions of different nitrogen speciation to BN and the relationship between nitrogen speciation and release flux. Results showed the spatial variations in all nitrogen forms influenced by hydrodynamic and lake topography. The TN in the whole lake was 735.91-2846.51mg/kg, with the mean value of 1371.85mg/kg. Specifically, the mean values of TN in East Dongting Lake, West Dongting Lake, South Dongting Lake and outlet of Dongting Lake were 1513.43,3.14,2.76and 1363.31mg/kg, respectively. The HN, NHN, and EN in sediments accounted for 66.74%, 21.46%, and 11.80% of TN, respectively. The mean values of BN in East Dongting Lake, West Dongting Lake, South Dongting Lake and outlet of Dongting Lake were 189.31,0.16,2.87and 139.51mg/kg, respectively, and BN was mainly influenced by EN and HN. The releases of ammonia nitrogen in East Dongting Lake, West Dongting Lake, South Dongting Lake and outlet of Dongting Lake were 6.32,7.03,7.78and 146.96mg/(m²·d), respectively, and were mainly affected by EN, especially for the exchangeable ammonia nitrogen. While HN and TN were not the main factors influencing the nitrogen release from sediments. The results could effectively support for the construction of hydraulic engineering and water environment models of Dongting Lake.