Abstract: Cellulose, pectin, starch and protein are some macromolecules with high content in tobacco leaf, which greatly affect the quality of tobacco leaf. In this study, bacteria were isolated from mellow tobacco leaves, and their enzyme production conditions and effects were studied, providing a new theoretical basis for microbial enzyme production in tobacco leaves and improving tobacco quality. In this study, strain 2-4A was screened, which was capable of producing amylase, pectinase, cellulase and protease at the same time. The strain was identified as Bacillus mojavensis. The activities of amylase, pectinase, cellulase and protease were increased to 41.36L, 3.64, 5.14 and 72.13 U/mL by optimizing the fermentation time, fermentation temperature, pH of medium and inoculum volume of strain 2-4A, respectively. After 72 h treatment with fermentation solution, the four macromolecular substances in tobacco leaves were degraded. The degradation rate of protein reached 37.8% and that of starch was over 30%. The degradation effects of pectin and cellulose were slightly weaker, but both were more than 10%. The contents of ketones, acids, esters, heterocycles, alcohols, aldehydes and other aroma substances in tobacco leaves were improved by the fermentation solution of strain 2-4A. Among them, acid and alcohol substances increased the most. In terms of single substance, the content of solanidone, phytol and 3-methylbutyric acid increased by 0.51%, 15.83% and 6.85% compared with that before fermentation. Bacillus mojavensis obtained in this study has the potential to be applied in improving the quality of tobacco leaves, and can be applied in the large-scale alcoholization process of tobacco leaves in the future.