Abstract: The microbes have an important impact on the transport and enrichment of I⁻ in groundwater, which in turn affects water security. Currently, most of the studies on microorganisms and I⁻ migration and enrichment are on the cultivation of specific microbial species in laboratory environments, and there are fewer studies on microbial communities and I⁻ in natural environments. In order to understand the structural characteristics of microbial communities in groundwater with different I⁻ concentrations, the microbial communities in groundwater with different I⁻ concentrations in the coastal area of Tianjin were analyzed. The research methods employed techniques such as Mantel test, alpha-diversity analysis, LEfSe analysis, co-occurrence network analysis, and PICRUSt2 analysis to examine the microbial data.. The results indicated that: (1) A total of 392 genus of 215 family of 122 order of 42 class of 23 phylum of bacteria with relative abundance >0.01% were detected in the groundwater, of which Proteobacteria, Bacteroidota, Campilobacterota, and Actinobacteriota were the dominant species in the microbial community. (2) Groundwater microbial communities were positively correlated with water chemistry environmental factors such as Na⁺, pH, TDS, Ca²⁺ and Mn²⁺. (3) The diversity, ecosystem complexity, and richness of microbial communities decreased with increasing I⁻ concentration gradient; with increasing I⁻ concentration gradient, the coverage of species expanded, the community structure gradually changed from aggregated to discrete, and the relative independence of each species increased. This study can provide some reference value for the research related to groundwater microorganisms and iodine in Tianjin and similar coastal areas.