Abstract: In order to optimize the quality of the formula module in the process of leaf re-roasting and realize the accurate utilization of tobacco, the chemical composition changes of different sizes of tobacco in the first threshing were systematically analyzed. Targeting tobacco raw materials from different ecological zones in China. Focusing on the primary leafing unit and its six air splits, the conventional chemical composition and differences of different sizes of cigarettes were measured and analyzed. The results showed that, 1)There are differences in the chemical composition of flue-cured tobacco from the first threshing of different ecological zones. 2)The size of the sheet has a significant impact on the chemical composition content. Large and medium lamina sizes exhibited largely consistent chemical compositions, whereas the chemical profile of scraps differed most significantly from the overall average. As lamina size decreased, total sugar, reducing sugar, and the sugar-to-nicotine ratio gradually declined, while total nitrogen, non-nicotine nitrogen, and the nitrogen-to-nicotine ratio progressively increased. 3) The most significant changes in the chemical composition ratio of tobacco flakes in zones V and VI indicate that there are significant differences in the quality of different types of tobacco flakes in these two production areas. 4) The quality rules of different types of cigarettes at each wind outlet indicate that, small lamina showed the smallest compositional deviation from the overall quality, while scraps exhibited the largest deviation. The third air separation point shows the greatest difference in quality between tobacco scraps and overall raw material. Regions VII and VIII demonstrated smaller overall compositional variations across sizes and outlets within the primary unit, whereas Regions V and VI showed larger variations. This study provides a theoretical reference for the quality control of formula modules and the utilization of differentiated tobacco resources.