Soil represents the largest organic carbon (C) pool in terrestrial ecosystems, and the regulatory mechanisms by which microbial communities influence carbon pool dynamics have emerged as a major focus in terrestrial carbon cycle research. In this study, sediments from check dams on the Ordos Plateau were analyzed to compare bacterial communities across two precipitation zones (250–300 mm and 350–400 mm), assessing their effects on the MBC/SOC and DOC/SOC ratios. Results indicated that in the 350-400 mm precipitation zone, total nitrogen(TN)and SOC contents were significantly greater than those in the 250–300 mm zone by 135.29% and 50.00%, respectively (p<0.001), whereas sand content significantly declined by 25.28% (p<0.01).In the 250-300 mm zone, Actinobacteriota (10.74%-37.16%)and Acidobacteriota (13.05%–18.61%) were predominant, with the combined relative abundance of Chloroflexota and Gemmatimonadota reaching 16.33%. In contrast, in the 350-400 mm zone, Proteobacteria was significantly enriched (24.62%-56.57%), accompanied by marked increases in Escherichia–Shigella (15.79%-25.28%) and Pseudomonas (3.35%-8.28%), leading to greater community dominance. In the low-precipitation zone, K-strategist bacteria (Actinobacteriota) dominated the community, facilitating carbon decomposition and reducing carbon stability, whereas in the high-precipitation zone, the community shifted toward r-strategist bacteria (Proteobacteria), enhancing carbon fixation functions, such as the Calvin cycle, and thereby decreasing DOC/SOC and MBC/SOC ratios. Elucidation of microbial mechanisms underlying carbon sequestration in check dam sediments within ecologically fragile areas is essential for improving terrestrial ecosystem carbon sink capacity and supporting national “carbon neutrality” strategies.