Abstract: Sansha Yongle Blue Hole is the deepest marine blue hole for the known ones in the world.Microorganisms play critical roles in this special ecosystem of the marine blue hole.In order to reveal the bacterial role in material cycle of the blue hole, the bacterial community characteristics in sediment from Sansha Yongle Blue Hole was detected using high-throughput barcoded pyrosequencing of 16S rRNA gene.There was a ledge with sediment in about 150 m depth, so the sediment samples were collected from the ledge (152 m and 162 m depth with 10 m distance) and the bottom of the blue hole (about 300 m depth).The bacterial population at three different depth was compared by analyzing sequencing data from Illumina Miseq.A total of 121 690 high-quality partial 16S rDNA sequences were obtained by Miseq sequencing analysis.Those sequences were assigned to 53 phyla, 301 genera and 546 species.The Shannon index at 152 m, 162 m and 300 m were 5.66, 5.72 and 5.55, respectively.Both the dominants and their relative abundance varied significantly at different depth, while some dominants were resemble and overlap.For example, both Chloroflexi and Proteobacteria were dominant phyla among the three samples, but their relative abundance varied significantly:the relative abundance of Chloroflexi was 44.73% at 152 m, 18.42% at 162 m and 4.98% at 300 m, while Proteobacteria was 13.29% at 152 m, 23.00% at 162 m and 44.88% at 300 m.Some bacteria participating in the sulfur cycle were found, such as Chlorobi, Desulfobacteraceae, Desulfatiglans, Desulfococcus, Thiomicrospira and so on, indicating that the sulfur cycle was very active in this marine blue hole.Otherwise the relative abundance of those bacteria was different clearly at the different depth, suggesting the step participating in sulfur cycle varied obviously.