Altitude offers a unique vantage point for studying how environmental changes affect the community structure and nitrogen fixation rate of soil nitrogen-fixing bacteria. Biological nitrogen fixation is an important source of bioavailable nitrogen in mountain ecosystems. However, the relationship between the community characteristics and nitrogen fixation rate and the altitude gradient of autogenous nitrogen-fixing bacteria remains unclear. In order to make up for this lack of understanding, this study determined the diversity of nitrogen-fixing bacteria and the variation of nitrogen fixation rate along the coastal uplift gradient of Sejila Mountain in southeast on the basis of sequential sampling (3700-4500 m) and analysis of nitrogen fixation genes (nifH) by high-throughput sequencing technology. The results showed that the α-diversity of soil nitrogen-fixing bacteria decreased with increasing altitude t along he 3700 m to 4500 m gradient of Sejila Mountain (P < 0.05).The community structure and soil properties of nitrogen-fixing bacteria changed significantly with the altitude gradient (P=0.001). The nitrogen fixation rate was significantly affected by altitude (P < 0.05). In addition, the α-diversity of nitrogen-fixing microbiota was mainly affected by the total carbon and total nitrogen content in the soil. The results of structural equation model analysis showed that the difference of altitude factor mainly affected the diversity of nitrogen-fixing bacteria, and then affected the nitrogen fixation rate. The results are helpful to enrich and improve the understanding of the diversity of soil nitrogen-fixing bacteria and the response of nitrogen-fixing flux to environmental changes in typical alpine forests in XiZang.