Abstract: To promote the openness of upper leaves of flue-cured tobacco K326 and increase its industrial usability, comparative experiments were conducted in the same fields distributed in 90 experimental plots in Yuxi. Gibberellin (GA3) was sprayed at topping stage, while water was taken as the control (CK). The effects of GA3 on the area, yield and chemical compositions of upper leaves of flue-cured tobacco in two types of fields (mountainous regions and dam lands) were analyzed. The results showed that spraying GA3 at topping stage promoted the openness, yield and quality of upper leaves in two types of fields. Comparing with CK, the average area of upper leaves in mountainous regions and dam lands expanded by 20% and 30%; the yields raised by 8.4% and 11.3%; and the proportion of high grade leaves increased by 2.3% and 4.3%, respectively. At the same time, the difference between total sugar and reducing sugar and nicotine content decreased, the contents of total nitrogen and potassium increased, and chemical components became harmonious in the two types of fields. The regression analysis indicated that the increase of tobacco leaf area was the main reason that GA3 promoted the yield and quality of upper leaves of flue-cured tobacco, and the altitude of planting area affected the increase of leaf area directly. With the rise of altitude, the average temperature at mature stage decreased, which indirectly influenced the contents of nicotine and potassium in upper leaves.