Bacterial diversity and community composition was investigated in the Lake Daihai Basin, Inner Mongolia using high-throughput sequencing technology. The results showed that bacterial diversity was highest in sediments, followed by river and lake water. Cluster analysis showed that bacterial community compositions in the inflowing river, lake water and sediments were separated into three distinct groups, indicating great differences in bacterial community compositions among the three habitats. Taxonomic annotation showed that the dominant bacterial flora in the river was Patescibacteria, Proteobacteria, Bacteroidetes and Actinobacteria. Actinobacteria was the most dominant bacteria phylum in the lake water, while the dominant bacterial flora in sediments were Proteobacteria and Chloroflexi. Canonical correspondence analysis and Monte Carlo permutation test revealed that the variations of bacterial community compositions in the river and lake were significantly explained by conductivity and suspended solids, which explained 86.5% of the variation. Redundant analysis and Monte Carlo permutation test revealed that the variations of bacterial community compositions in sediment were significantly explained by depth, magnetic susceptibility and total organic carbon, which explained 47.9% of the variation in total. During the past 30 years, Lake Daihai has experienced salinization in lake water and a remarkable increase of carbon and nitrogen in the sediment due to climate change and anthropogenic activities. The variations of bacterial diversity and community composition in the water and sediments, as well as their main driving environmental factors, highlight the responses of bacteria to the combined effects of climate change and anthropogenic activities on Lake Daihai.