Abstract: In this study, an in-situ enrichment in depth of 3 300 m in the South China Sea was newly developed for 17 months by adding slowly releasing ammonium, nitrate and urea into a circulation chamber of a deep-sea water incubation system. The response of microbial community was analyzed combining with Miseq high-throughput sequencing technology and the lab seperation. Our results showed that γ-Proteobacteria is the most abundant in the bacterial population. The bacterial composition on genus level differed obviously in the cotton samples and water samples in the circulation chamber, where Shewanella spp. and Colwellia spp. are the main members, respectively. Thaumarchaeota dominated in the archaea domain with a high proportion of the ammonia oxidizing archaea (AOA). Culture results showed that a total of 17 bacterial strains were isolated from the in-situ samples, including Halomonas, Marinobacter,Sulfitobacter and so on.The in-situ enrichment in the South China Sea was further selectively enriched in laboratory under different initial nitrogen sources (ammonia, nitrate, nitrite) and temperatures (28℃ and 10℃). A total of five secondary enrichments were obtained. The enriched consortia exhibited a strong nitrogen removal capacity, by releasing N₂O or N₂ as the end products, indicating their denitrification ability. Bacterial community analysis of the secondary enrichments showed that Halomonas became the dominant bacteria, followed by Marinobacter and Idiomarina. Among them Halomonas and Idiomarina were successfully isolated and Halomonas was further confirmed of aerobic denitrification ability.