Abstract: To investigate the distribution and quality change of different size tobacco strips separated by different threshing and pneumatic separating units, leaves of C2F grade of flue-cured tobacco grown in Sichuan in 2021 were taken as the research sample to systematically analyze the differences in strip flow and structure among different threshing and pneumatic separating units. The differences in chemical composition and sensory quality among different size strips were also analyzed. Meanwhile, the usability of tobacco strips of different sizes was evaluated with Chemical Component Usability Index (CCUI). The results showed that: 1) With the increase of threshing unit stages, the flow and size of tobacco strips decreased gradually, and tobacco scraps and small-sized strips were relatively easier to be separated by the first-stage pneumatic separators in all the threshing units. 2) The chemical component usability of tobacco scraps was significantly lower than that of large-, medium-and small-sized strips, and the usability raised gradually with the increase of threshing unit stage. However, there was no significant change in large- and medium-sized strips. 3) The sensory quality of tobacco strips of different sizes raised first and then reduced with the increase of threshing unit stage. The best sensory quality of large- and medium-sized strips appeared in the second-stage threshing unit, while that of small-sized strips and tobacco scraps appeared in the third-stage and forth-stage threshing units respectively. The above results provide a technical guidance for the industrial application of fine classification and differential blending of tobacco strips in threshing and redrying process.