Abstract: In order to study the effects of processing conditions on the change of chemical components in tobacco, different conditions of conditioning and storing were simulated in laboratory and their effects on the main carbohydrates (including total sugar, reducing sugar, and starch) and sugar/nicotine ratio in different grades of tobacco leaves were orthogonally experimented. The results showed that: 1) tobacco grade was a highly significant influencing factor while comparing with process conditions; the effect of storing circumstance on the contents of total sugar (α=0.10) and reducing sugar (α=0.05) was significant; 2) the significant factors (α=0.10) affecting the content of starch was storing time followed by the moisture content in conditioning; 3) the significance factors (α=0.05) in order of the degree affecting the ratio of total sugar to nicotine was storing circumstance > storing time > conditioning temperature.