To elucidate the spatiotemporal succession patterns and environmental driving mechanisms of bacterial communities across different habitats in reservoirs within the semi-arid region of southern Ningxia, water and sediment samples were collected from eight typical reservoirs in Guyuan City during April, July, and October 2025. By integrating 16S rRNA gene high-throughput sequencing with the Trophic Level Index (TLI), Mantel tests, and Redundancy Analysis (RDA), this study investigated community structure, seasonal dynamics, and their relationships with environmental factors.The results indicated that the eight reservoirs exhibited a complete environmental gradient ranging from mesotrophic (Site S6) to hyper-eutrophic (Site S1) status based on TLI evaluation. Proteobacteria was the predominant phylum in both water (31.68%–36.49%) and sediment (38.16%–43.48%) habitats. In July, high temperatures and strong irradiance drove an explosive enrichment of Cyanobacteriota and its constituent order Synechococcales in the water column, resulting in a simplified community structure and a decline in α-diversity. In contrast, the sediment habitat remained relatively stable, enriching benthic-specific taxa such as Acidobacteriota and Chloroflexi, with α-diversity exhibiting a trend of seasonal accumulation.The environmental driving mechanisms demonstrated distinct habitat specificity. Water bacterial communities were significantly influenced by Total Nitrogen (TN), Total Phosphorus (TP), Permanganate Index (CODMn), and Nitrate Nitrogen (NO3-N) (P<0.01), while high summer temperatures and pH were identified as key physical factors reshaping community structure. Conversely, the succession of sediment communities was primarily regulated by Ammonium Nitrogen (NH4+-N), TP, and Salinity (SAL). This study systematically elucidates the seasonal variations in microbial community structures across different habitats in arid-region reservoirs, providing a scientific basis for regional water environment management.