Forest fires can cause an increase in soil temperature, alter physicochemical properties and enzyme activity, thereby significantly affecting soil microbial communities. A comprehensive investigation into the composition of soil microbial communities in Pinus tabulaeformis forests following different fire severities is crucial for understanding the mechanistic impacts of fire on soil biological activity within these ecosystems. This study focused on Pinus tabulaeformis forests in Qinyuan County, Shanxi Province, for 4 years post-fire, involving the collection of soil samples from two depths (0-10 cm and 10-20 cm) following different fire severities (light, moderate, and severe) and unburned conditions. The analysis included soil physicochemical properties, enzymatic activities, and microbial community composition. Relative abundance and linear discriminant analysis effect size were used to identify key microbial taxa contributing to the observed differences in community across fire severities. The Mantel's test and redundancy analysis further clarified the influence of fire on microbial communities through the lens of soil environmental factors. The results showed that: (1) Different fire severities significantly impacted soil physicochemical characteristics and enzymatic activities. In the 0-20 cm soil layer, both pH and bulk density demonstrated a positive correlation with fire severity. Within the 0-10 cm soil layer, organic carbon, total nitrogen, alkaline phosphatase, and catalase initially increased but then declined as fire severity rose, while urease activity exhibited a consistent decrease with increasing fire severity. (2) At the phylum level, the bacterial community was dominated by Proteobacteria, Actinobacteria and Acidobacteria. At the class level, the fungal community was dominated by Agaricomycetes, Eurotiomycetes and Sordariomycetes. Following fire, Actinobacteria showed an increased relative abundance compared to the control, while both Proteobacteria and Acidobacteria experienced declines. The relative abundance of Agaricomycetes increased but then declined as fire severity rose, and after severe severity, Eurotiomycetes and Sordariomycetes were dominant. (3) Soil organic carbon was an important factor affecting soil microbial community composition. Soil organic carbon and pH were the factors that significantly affected the bacterial dominant phylum, and bulk density and organic carbon were the factors that significantly affected the fungal dominant class. In conclusion, the soil fungal community demonstrates a higher sensitivity to fire impacts compared to the bacterial community, with organic carbon serving as a primary driver of microbial community dynamics.