Abstract: In order to explore the relationship between the biosynthesis and catabolism of terpenoids in flue-cured tobacco of different maturity levels and the intrinsic quality of tobacco leaves, using Zhongyan 100 as the test material, real-time fluorescence quantitative PCR (RT-PCR) technology was used to measure the expression levels of key genes for terpenoid synthesis and degradation, and gas chromatography-mass spectrometry (GC-MS) detection technology was used to detect terpenoids and their degradation products after modulation and processing. At the same time, the smoking quality of tobacco leaves was evaluated. The results showed that as maturity increased, the shedding of glandular hairs intensified, the content of carotenoids and the expression level of PAL gene increased gradually; The content of siberians and genes expression level of DXR, CYP71D16, C4H, CHS showed a "increase first and then decrease" trend, and reached the peak during the ripening period. The sensory quality evaluation of the fully mature tobacco leaves in the middle and upper parts was the best. Maturation was found to be closely related to the upregulation of gene expression related to the synthesis of terpenoids, playing a role in softening smoke and improving quality and aroma. In tobacco production, it is recommended to further delay the harvest of tobacco leaves by 5-7 days on the basis of mature harvest, so that the maturity of the tobacco leaves can reach fully maturity, which can effectively improve the intrinsic quality and industrial usability of middle and upper tobacco leaves.