The Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis) is a subspecies of finless porpoise and is known to live only in the middle and lower reaches of the Yangtze River and the adjacent Dongting and Poyang Lake. Since the 1990s the population has decreased dramatically due to habitat degradation, by-catch, water pollution and other human activities. The Yangtze finless porpoise was listed as an Endangered species on the IUCN Red List since 1996 and was listed as a top-level protected animal in China since 1989. The Dongting Lake, China's second largest freshwater lake, is located in the northern Hunan Province. The lake is at the south of the middle reach of Yangtze River and is divided into three parts:East Dongting Lake, South Dongting Lake and West Dongting Lake. Dongting Lake is important both at home and abroad due to the aquatic biodiversity, geographical location, and human activities. Dongting Lake has been for hundreds of thousands of years as one of the most important habitats for Yangtze finless porpoise. According to the population assessment by the Ministry of Agriculture and Rural Affairs in 2017, there are approximately 110 individuals (10.87% of the total population) living in Dongting Lake. To assess the population distribution of the finless porpoise and its relationship with fish density, 54 line transects surveys and eight hydroacoustic surveys were conducted in East Dongting Lake covering four hydrological seasons between June 2012 and December 2017. A total of 1110 individuals were observed, and they were primarily distributed in an elongated area approximately 35km long between Xiangyin County and Dongting Bridge. The natural habitat area of finless porpoise estimated by the method of minimum convex polygon (MCP) under the 100%, 95%, 75%, and 50% were 161.3km², 114.3km², 77.0km² and 64.3km² respectively, accounting for 24.2%, 17.1%, 11.5% and 9.6% of the whole finless porpoise protected area. Results of the one-way ANOVA revealed significant differences among observations during different hydrological seasons (P<0.05) and the highest frequency of groups and individuals of finless porpoise were observed (13.92±4.64 groups/survey and 31.92±7.17 ind./survey) during the dry season. The lowest frequency (5.17±1.64 groups/survey and 17.25±7.46 ind./survey) occurred during the wet season. Results of the hydroacoustic surveys showed that the highest fish density was 57.21ind./1000m³ in March 2013. There was a weak negative correlation (R =-0.601, P>0.05) between fish density and water levels in East Dongting Lake. ArcGIS modelling and hydroacoustic technology were combined to analyze the spatial distribution of fish densities, and the results showed that fish mainly distributed in Bianshan-Meitanwan (Area III), Meitanwan-Lujiao Port (Area IV) and Lujiao Port-Nianyukou (Area V) during low water (dry season and late stage of falling season). Fish were more disperse during high water. During low water of Dongting Lake, an uneven distribution of fish was found and significant differences existed between Area III and other areas (P<0.05) with the highest fish density (107.52±17.36 ind./1000m³). Except for the significant differences between Nianyukou-Leishi Port (Area VI) and Chenglingji-Dongting Bridge (Area I), and Area III (P<0.05), there were no significant differences between the other areas (P>0.05). The positive relationship between the number of porpoises and fish density (R²=0.86, P<0.01), analyzed by Pearson correlation, suggests that Yangtze porpoise possesses the behavior to track fish school. Future conservation on the Yangtze finless porpoise could be more effective if special measures are conducted to stop fishing and habitat degradation related to finless porpoises in East Dongting Lake.