Abstract: In order to realize the regularity of main chemical compositions changing in curing process and establish the appropriate curing hour for sun-cured tobacco, studies were taken at the dynamic changes of main chemical compositions at stacking stage, the results showed that most of starch in the leaf is degradative in the period of stacking. Total sugar increases rather fast after stacking has begun. The change of total sugar and starch content is contrary and has a significant negative correlation, the correlation coefficient r=-0.89. Both total nitrogen and nicotine content in leaf at the end of stacking stage change less compared with those before stacking. Longer stacking is in favor of coordination of chemical compositions in tobacco leaves and improving the quality of cut tobacco. The appropriate stacking hour for cutters and upper leaves should be at least five days.