Abstract: Poyang Lake is an important freshwater, sand and stone source area in China, where its sublacustrine sedimentary topography has always drawn much attention in academia. This study systematically investigates the underwater topography and sedimentary characteristics of Poyang Lake with sub-bottom profiler. Data analysis of 32 survey lines revealed that the depth of Poyang Lake varies from 0.16 m to 23.71 m, with the water channel into Yangtze River and the northwest part of the main lake area being relatively deeper. The thickness of unconsolidated sediment varies from 0 m to 8.73 m, with thick layers concentrating in the central part of the main lake area, and the estimated volume of the unconsolidated sediments is approximately 3.02 km³. In September 2022, shallow drilling exploration is conducted in the main lake area to verify the reliability of the data from sub-bottom profiler. Comparison with previous studies indicates that large-scale sand mining can significantly impact the bottom topography of Poyang Lake. This study comprehensively reveals the current state of underwater topography and sedimentary characteristics of Poyang Lake, and the conclusion is useful for the relevant research and management.