[Objective] Soil environmental factors are highly spatially heterogeneous, especially soil pH, nutrient availability, soil temperature and soil microbes, which vary with soil depth, and hence affect the distribution of soil microbial communities. Soils in deep soil layers may have microbial communities that have adapted to the environments of deep soil layers, and consequently are different in structure from those in topsoil layers. Microbial communities decrease in biomass and diversity with depth in the soil profile, which alters structures of the soil microbial communities and affects their functions. Microbes in deep soil play an important role in soil formation, biogeochemical reactions and pollutant degradation. So deep soil has significant influences on quality indices of the soil and hence productivity of the vegetation on the surface. Interactions between species of the microbes may be more important than richness and diversity to ecosystem function of the microbial community, especially in complex ecosystems. Interactions between microbial communities are a part of the microbial network of a terrestrial ecosystem, and the basis of biochemical cycles. Ecological network analysis is a new analysis method to visualize interactions between microbial communities and explore co-existence patterns of the species in microhabitats and their main influencing factors. Network analysis can be used to explore mechanisms of microbial interactions driving biogeochemical coupling of important elements in soil, and hence is an important means to improve service functions of a soil ecosystem. However, most of the previous studies on soil microbial communities focused on those in the topsoil (0-20 cm) layer or on abundance of microbial species. Therefore, the information available in the literature about potential relationships between microbial interactions and soil depth, and their determining environmental factors.[Method] After late rice was harvested, soil samples were collected from a paddy field in Yingtan (116°54' E, 28°13' N, 34-62 m in elevation), South China. For the sampling, five sampling sites were set randomly as five replicates. At each site, a soil sample was collected from each of the five soil layers, 0-10, 10-20, 20-40, 40-60, 60-80 and 80-100 cm with an auger, making up a total of 30 samples for analysis, separately, of soil geochemical properties and DNAs.[Result] Contents of soil nutrients, including total nitrogen (TN), total carbon (TC) and NH₄⁺-N, and species richness of soil microbes decreased significantly with soil depth. Network analysis shows that with increasing soil depth, the average. number of neighbors, clustering coefficient and Network density of the microbial interaction network increased, indicating that the associations between microbial communities became more complex in the microbial co-existence network with positive interactions intensified, and interactions within the bacterial community and within the fungal community enhanced, but the interactions between bacteria and fungi communities reduced. TC and TN were the main factors contributing to soil microbial interactions according to the random forest analysis. Variance partitioning analysis of the soil microbial network shows that microbial interactions were affected by carbon (TC + DOC) and nitrogen (TN + NO₃^--N+NH₄⁺-N). Moreover, the effect of C intensified with soil depth.[Conclusion] The interactions between soil microbes become more intensive, more complicated and more modular with soil depth. The interactions within soil microbial communities are positively related to soil depth, and so were the interactions between bacterial and fungal communities. With the soil going down in depth, the contribution of soil C increased from 3.58% to 32.67% for the microbial interaction network.