Abstract: Pot experiment was carried out to study physiological change and matter accumulation of flue cured tobacco leaf in the course of mature with different K nutrition levels. The results showed that application of K fertilizer could be promoted maturity, prolonged the aging, increased the accumulation of dry matter and improved some physiological and biochemistry properties. The physiological index such as relative electric conductivity, POD activity and free proline were increased with the increasing K rates. The results also indicated that application of K fertilizer, the transformation of organic substance in tobacco leaf was fully and potassium contents in leaves enhanced, and the sugar/nicotine ratio was in a moderate degree. Therefore, application of K with a suitable rate for improving the qualities of tobacco leaf is importance.