As the deepest oceanic trench currently known on earth, the Mariana Trench breeds unique bacterial community structure and diversity characteristics due to its deep-sea extreme environment such as oligotrophy, high pressure, low temperature, and low oxygen. In this study, oligotrophic media were selected for liquid co-culture of seawater and surface sediment samples from the Mariana Trench, and the samples were taken at different culture times for high-throughput sequencing, in which way we analyzed the dynamics of bacterial community structure composition and diversity as well as explored the possible interactions among microorganisms. The results showed that a total of 19 phyla, 34 classes, 76 orders, 131 families, 227 genera of bacteria were detected in the liquid co-culture samples, among which Proteobacteria and Bacteroidetes were the dominant taxa, followed by Firmicutes. Compared to the others, the seawater sample collected from 1000 m below sea level had the highest bacterial community diversity and the higher relative abundance of Cyanobacteria. The bacterial richness, diversity, and community structure in the co-culture samples all changed with culturing time, and there was especially higher bacterial community diversity in the middle stage of co-culture samples. In the surface sediment samples, Halomonas occupied a dominant position in the late stage of co-culture probably due to its strong competitiveness. Gene function prediction and metabolic pathway enrichment showed that with the increasing time of co-culture, the abundance of metabolic pathways associated with microbial growth decreased significantly, while the abundance of metabolic pathways related to microbial interactions increased significantly. The diversity of bacterial community detected in co-culture samples was much higher than that of the isolated culture samples, and only a small number of bacteria genera were identified by both culturable methods and liquid co-culture in common. In conclusion, there are microbial interactions such as competition and mutualistic symbiosis in the bacterial community of the Mariana Trench, and the liquid co-culture method is beneficial to reveal the bacterial interactions. This study provides a theoretical basis for the composition and maintenance of microbial ecosystems in extreme environments like hadal environments and deep-sea, and also provides scientific guidance for the further study on the survival strategies of extremophile.