Forest fire burning will lead to an increase in soil temperature, change physicochemical properties and enzyme activity, and thus have a significant impact on soil microbial communities. A comprehensive investigation into the composition of soil microbial communities in Pinus tabulaeformis forests after varying fire severities is essential for elucidating the mechanistic effects of fire on soil biological activity within these ecosystems. This study focused on the Pinus tabulaeformis forests in Qinyuan County, Shanxi Province for 4 years after fire, and involved collecting across two soil depths (0-10 cm and 10-20 cm) after different fire severities (light, moderate, and severe) and unburned. Analysis included soil physicochemical properties, and enzymatic activities, and microbial community composition. The relative abundance and linear discriminant analysis effect size were conducted to identify key microbial taxa contributing to observed differences in community across fire severities. The Mantel's test and redundancy analysis further elucidated 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.