Abstract: Tiegang Reservoir is an important drinking water source reservoir in Bao'an District, Shenzhen. In order to understand the status of fish resources in this reservoir, we combined a combined method of underwater acoustic detection and net sampling to investigate the current fish resources and community structural diversity in October 2024. During the investigation, a total of 19 species of fish were collected, belonging to 6 families and 17 genera. Among them, the Cyprinidae fish accounted for the highest proportion (57.89%). The dominant species were Oreochromis niloticus, Coilia grayii, Carassius auratus, Aristichthys nobilis and O. mossambicus. The number of C. grayii was the highest (24.97%), and the biomass of A. nobilis was the highest (24.55%). Underwater acoustic detection indicated that the average density of fish resources was 2.43 ind·m⁻², with a total of approximately 20.82 million fish. The majority of the fish were small-sized ones with body lengths ranging from 1 to 10 cm (Accounting for 96.07%). In terms of horizontal distribution, the fish resources density was higher in the central area; in terms of vertical distribution, the fish were mainly distributed in the water layer with a depth of 5‒13 m. This study is the first to assess the structural characteristics of the fish community and fishery resources in the Tiegang Reservoir in Shenzhen. The results can provide basic data support for the adjustment of fishery resource structure, sustainable utilization and ecological protection of reservoirs.