In order to study the variation of size distribution of tobacco strips from different threshing and separation unit, an upper blend tobacco formula was introduced into threshing machine with five stages of threshing unit and eleven pneumatic separators. The results showed that the size proportion of tobacco strips separated from different pneumatic separators exhibited a similar change trend. Moreover, in the first and second stage threshing unit, the large and middle size particle content could reach more than 94% with good stability. Meanwhile, the characteristic size tobacco strips and the proportion of tobacco strips with size bigger than 44.5 mm increased with pneumatic separation stage for the threshing units of the first and second stages. However, in the threshing units of the third and forth/fifth stages, the characteristic size tobacco strips and the proportion of tobacco strips with size bigger than 44.5 mm decreased dramatically, accompanied with a significant increase in proportion for small size tobacco strips. Furthermore, the characteristic size of strips collected from different threshing and separation unit and the corresponding uniformity of tobacco strips size were both decreased with stages of threshing unit.