Abstract: 【Objective】To study the abundance and structure of nitrogen-fixing microbial community in different amendment application in acidic tobacco-planting soils,and to provide a scientific basis for selecting the amendment and applied in flue-cured tobacco production from a microbiological point of view.【Method】Open-field random test involving a single factor was performed. Four soil conditioner treatments were set,namely,silicon-calcium-potassium-magnesium(T1),dolomite(T2),silicon-calcium-potassium-magnesium and biochar(T3),dolomite and biochar(T4). The treatment without soil conditioner was the control(CK). Agronomic traits were investigated during the exuberant growing period,and rhizosphere soil samples were collected. The fluorogenic quantitative real-time PCR technique was adopted in the experiments using the high-throughput sequencing platform to target the nifH gene. The abundance,nitrogen-fixing microbial community composition in acidic tobacco-planting soils werestudied under different treatments. The driving factors for structural changes in the diazotrophic communities of the soil were identified.【Result】The application of different soil conditioners generally improved the agronomic traits of tobacco plants and soil pH value,organic carbon content and C/N ratio. Soil conditioners significantly improved the nifH gene abundance in soil nitrogen-fixing bacteria(P<0.05,the same below). T1,T2,T3 and T4 treatments achieved 2.97,3.32,4.68 and 3.81 times increase compared with CK,respectively.Soil conditioners also increased the α-diversity index of the soil nitrogen-fixing bacterial community. Of all treatments,T3had the highest Chao1,ACE,Shannon and Simpson indexes. The results of correlation analysis showed that the abundance of nitrogen-fixing microbial community,Chao1 and ACE indexes were significant positively correlated with soil pH. On the phylum level,five phyla were identified. Proteobacteria,Cyanobacteria,and Firmicutes were dominant phyla.In contrast,the amendment addition altered the nitrogen-fixing microbial community structure with shifts in the phyla and dominant genus,with significantly higher Proteobacteria,Cyanobacteria,Bradyrhizobium and Azospirillum in the siliconcalcium-potassium-magnesium and biochar. Soil p H,organic carbon,nitrate nitrogen and C/N were the key factor correlated with change in nitrogen-fixing microbial community structure. The results from redundancy analysis showed that soil pH,organic carbon,nitrate nitrogen and C/N were the key factors correlated with change in nitrogen-fixing microbial community structure.【Conclusion】Mixed application of silicon-calcium-potassium-magnesium and biochar has multiple effects:alleviating soil acidification,improving tobacco field environment,promoting tobacco plant growth,and increasing nifH gene abundance,α-diversity index,and relative abundance of dominant species in soil nitrogen-fixing bacteria. This fertilizer combination is worthy of wider application in acidic tobacco-growing soils.