Abstract: In order to study the effects of Bacillus subtilis on the chemical composition and sensory quality of tobacco leaves, a microorganism (H11) was screened from the cured tobacco leaves. Through strain morphology and 16S rDNA sequence analyses, H11 was preliminarily identified as Bacillus subtilis subsp. subtilis. It was used to ferment 20 kg low-grade tobacco leaves(2017 DCFB) from Pingdingshan County, Henan Province for 30 h, and the variations in sensory quality, routine chemical components and neutral aroma components of tobacco leaves before and after the fermentation were comparatively analyzed. Metagenomic sequencing technology was adopted to analyze the changes in microbial population on the tobacco leaves before and after fermentation, and the roles of enzymes in the leaf fermentation were discussed. Compared with no fermentation, the fermentation promoted the volatility, sweet taste, aroma quality and aroma quantity of tobacco smoke, increased the contents(mass fraction)of water-soluble total sugar and reducing sugar by 2.52% and 1.92% respectively, raised the contents(mass fractions) of neutral aroma components such as (E)-β-damascenone, dihydroactinidiolide and megastigmatrienone C by 25.92%, 10.57% and 12.15% respectively. The amounts of microorganisms on the tobacco leaves decreased significantly after fermentation, and the relative abundance of Bacillus increased to 76% of the total amount of microorganisms. Bacillus subtilis has important influences on the chemical composition and sensory quality of tobacco leaves, and it is characterized by a short fermentation time and high throughput, which can provide references for the microbiological treatment of low-grade tobacco leaves.