Climate change impairs organic matter decomposition and nutrient cycling in arid-region paddy soils, yet the microbial mechanisms underlying exogenous carbon-iron (CFe) interactions remain unclear. We investigated how combined additions of exogenous carbon (biochar/straw) and iron (ferrihydrite) modulate soil physicochemical properties, extracellular enzyme activities (EEAs), and microbial communities in paddy fields from the Yellow River irrigation area. Compared with the CK, CFe coupling significantly reduced soil pH while elevating Fe2+ and Fe3+ levels and enhancing the bioavailability of soil organic carbon (SOC) and total nitrogen (TN). The straw + ferrihydrite (SF) treatment most effectively promoted TN accumulation and Fe speciation transformation, and notably increased the activities of beta-1,4-N-acetylglucosaminidase (NAG) and catalase (CAT). The biochar + ferrihydrite (BF) treatment induced the highest activities of beta-glucosidase (BG) and alkaline phosphatase (ALP), both of which were strongly and positively correlated with SOC and Fe3+. CFe synergy alleviated anaerobic suppression of EEAs via a redox-mediated "iron gate" mechanism, primarily regulated by SOC, Fe2+, and Fe3+. Both BF and SF significantly increased the alpha-diversity of the prokaryotic community, as indicated by the Chao1 (increases of 3.34 % and 2.65 %, respectively) and Shannon indices (increases of 12.59 % and 10.60 %, p < 0.05). SF enriched facultative anaerobes (e.g., Chloroflexi), whereas BF favored oligotrophic Patescibacteria. Partial least squares structural equation modeling (PLS-SEM) revealed that microbial diversity was positively driven by EEAs and soil properties, whereas the relative abundances of specific phyla and genera exerted negative effects. Our findings demonstrate that CFe interactions regulate microbial diversity through direct enzymatic stimulation and indirect shifts in community structure, providing actionable insights for optimizing carbon sequestration and nutrient management in arid agroecosystems.