Abstract: In order to improve the intrinsic quality and utilization rate of tobacco stems, lignin content (mass percentage) was used as an index to study the effects of reaction temperature and time of ozonation pretreatment and moisture content in tobacco stem, due to the fact that lignin is a cell wall substance that has a great influence on sensory quality. The ozonation pretreatment parameters were optimized accordingly. The differences in microstructure, chemical components, aroma components and sensory quality of tobacco stem before and after the ozonation pretreatment were compared. The results showed that: 1) The reaction temperature, moisture content in tobacco stem, and the reaction time all had significant effects on the lignin content in tobacco stem. The lignin content decreased with the increase of the reaction temperature, moisture content in tobacco stem, and reaction time. The optimum reaction conditions for the ozonation pretreatment of tobacco stem lignin were 35 ℃, 120 min reaction time, and 40% moisture content. Under the optimized conditions, the lignin content decreased by 2.58 percentage points, with a decrease of 55.60%. 2) After the ozonation pretreatment, the surface wax of the tobacco stem disappeared, the collenchyma tissue was arranged disorderly, the conduit was broken and obviously damaged, and the wood fiber structure was broken. 3) The contents of total sugar, total vegetable alkali and protein decreased by 13.08%, 18.27%, and 8.26%, respectively; the reducing sugar content and nitrogen/nicotine ratio increased by 8.40% and 16.36%, respectively; and the other indexes did not change significantly. 4) The content of aroma components in tobacco stem changed greatly, the total amount increased from 136.719 to 159.376 μg/g, and the contents of neophytadiene, esters and acids increased significantly by 306.07%, 78.41% and 40.24%, respectively. 5) Compared with the control, the aroma of cut tobacco stems after the ozonation pretreatment and the cigarette containing them were enhanced, the offensive odor and irritation were significantly reduced, the aftertaste and sensory quality were improved. The quality and utilization rate of tobacco stems could be promoted by the ozonation pretreatment.