The variation in microbiota during pit fermentation is the main reason for the distinct characteristics of the 7 types of base Baijiu in jiang-flavor Baijiu (JFB) brewing. However, the specific structure, succession, and functional differentiation of microbial communities across different fermentation rounds remain unclear. Therefore, this study compared the differences in microbiota structure, environmental factors driving community assembly, and functional differentiations throughout 1–7 rounds (JC1–JC7) of pit fermentation in JFB production. Results showed that Lactobacillus dominated all rounds and complied with declining relative abundance from rounds JC1–JC7. The mould composition was similar in JC3–JC5 while the yeast structure in JC4 was found intermediate between JC3 and JC5. LEfSe analysis unveiled aroma-producing microorganisms as prominent biomarkers in JC1, strong enzyme-producing attributes in JC2, JC6, and JC7 biomarkers, and an enzyme and aroma-producing focus with robust tolerance in JC3–JC5 biomarkers. Acidity mainly regulated the microbial community in the first 4 rounds, with nutrient limitation drove microbial succession from the fifth round onward. Functional predictions underscored enriched amino acid metabolism enzymes in JC6 and JC1, while carbohydrate degradation exhibited predominant enzymatic profiles in JC2, JC6, and JC7. This study laid a foundation for comprehending community composition, succession, and flavor regulatory mechanisms throughout JFB brewing.