In order to clarify the changes of main non-volatile organic acid concentrations and metabolism related enzymatic activities in the process of the growth of flue-cured tobacco leaves,we used 12 flue-cured tobacco varieties to study the dynamic changes of total organic acid content,malic acid content,citric acid content,metabolism related enzymatic activities,the nicotine content and sensory quality of modulated smoke sample.The results showed that:(1)With the growth of tobacco plants,flue-cured tobacco total organic acid content indicated a trend of first increased and then decreased,in the middle of leaf age 50～60 d reached the highest value.The total organic acid content of different flue-cured tobacco variety middle leaves had significant differences in different age periods,while had little changes before and after modulation.(2)Malic acid content had a trend of gradually growth.Citric acid content displayed a slow “increase-decrease” trend.Malic acid content and the NAD-MDH(malic dehydrogenase) activity had a significant negative correlation.Citric acid content and the CS(citrate synthase) activity had a significant positive correlation,while had little correlation with the NAD-IDH(isocitrate dehydrogenase) activity.(3)When the total organic acid content was more than 32%,nicotine content was between 1.5% and 2.6% at the same time,the higher “acid-base ratio”,the better sensory quality of flue-cured tobacco.In summary,the accumulation of malic acid and citric acid in flue-cured tobacco leaf were regulated by the changes of its metabolism related enzymatic activities.“Acid-base ratio” influenced the smoke mildness of flue-cured tobacco.Through regulating NAD-MDH and CS activities to adjust the contents of malic acid and citric acid,coordinating “acid-base ratio” and improving the quality of tobacco.