Abstract: Blending modules of different leaf quality categories from southwest China tobacco growing regions in 2021 crop year were taken as the research samples to investigate the variations in chemical compositions of tobacco strips after industrial grading and separated by different pneumatic units. The chemical compositions of different leaf strip sizes were analyzed separately and systematically, and the results were compared between the blended modules. The Chemical Composition Usability Index (CCUI) of flue-cured tobacco was used to evaluate tobacco strips of different sizes. The results showed that: 1) The harmony in chemical composition of the tobacco strips thus separated and sorted was significantly lower than that of the strips separated by threshing procedures. 2) Among the different sized tobacco strips separated by threshing procedures, the chemical composition harmony of tobacco scraps was lower than that of large, medium, and small sized strips. With the increase of threshing procedures, the differences in reducing sugar content and sugar/nicotine ratio between tobacco scraps and different sized tobacco strips gradually decreased. 3) The blending modules with lower quality categories had greater potential to improve their quality by screening out tobacco scraps. 4) The large and medium strips separated by the second and third stage threshing units had better blending usability.