Abstract: Environmental DNA (eDNA) analysis has become an important tool for biological resources research. Sebastiscus marmoratus, an important coral reef fish in Zhoushan coastal waters, has high economic value. To explore the relationship between the density of cultured Sebastiscus marmoratus and its eDNA, this study analyzed the COⅠ gene sequence of Sebastiscus marmoratus and other five relative species based on a set of specific primer and probe. Based on K2P model, the interspecific genetic distances between Sebastiscus marmoratus and other species were calculated with the maximum value of 0.3202 between Sebastiscus marmoratus and Inimicus japonicus and the minimum value of 0.2617 between Sebastiscus marmoratus and Sebastiscus tertius. 2, 4, 8, 16 and 32 individuals with average weight of 12.46 g were respectively cultured in five indoor buckets with a volume of 1 m³, and 20, 40 and 80 individuals were respectively in three outdoor ponds with a size of 40 m×15 m×0.3 m. The samples were taken at 0, 8h, 16h, 1d, 1.5d, 2d, 3d, 4d, 5d, 6d, 7d, 8d and 10d for extracting eDNA. It was concluded that eDNA reached a stable stage after 3d and 7d indoors and outdoors respectively. By fitting the linear correlation function between culture density and eDNA concentration at the stable stage, a highly significant positive correlation was found between culture density and eDNA concentration under the two culture conditions (P<0.001, R²≥0.9546). The increase in eDNA concentration was higher in all indoor groups than that in the outdoor groups. This study provides a basis for eDNA monitoring and evaluation of Sebastiscus marmoratus resources.