In order to improve the air-curing quality of tobacco leaves，Yunxue No.2 was used to study the changes and correlation between non-structural sugars and plastid pigments during the yellowing stage of cigar tobacco leaves under different air-curing humidities.The changes in the intrinsic chemical composition of cigar tobacco leaves during the yellowing stage under conditions of an ambient temperature of 28℃ and ambient humidity of 90% （high humidity）， 80% （medium humidity）， and 70% （low humidity）.The results showed that the content of plastid pigments and starch in tobacco leaves had an overall decreasing trend， while the content of glucose， fructose， and sucrose had an overall increasing trend Under different air-curing humidities.The degradation rate of the content of chlorophyll in tobacco leaves treated with high humidity （yellowing humidity of 90%） was slow， but the cycle of degradation was long， while the content of chlorophyll in tobacco leaves treated with high and medium humidity after 96 hours of yellowing tended to a lower level， and the change was not significant.Low humidity （yellowing humidity of 70%） treatment significantly increased the accumulation in the content of glucose and fructose at the early stage of yellowing， and the increase was relatively small after 144 hours of yellowing.The trend of changes in the content of glucose and fructose treated with medium and high humidity was opposite to that with low humidity， with no significant increase at the early stage of yellowing， but a significant increase after 144 hours of yellowing.The trend of changes in the content of starch and sucrose under different treatments was almost the same.The results of correlation analyses showed that the changes in the content of plastid pigments and non-structural carbohydrate during the air-curing process reached significant or extremely significant levels.It is indicated that the rate of yellowing in tobacco leaves under the low humidity （yellowing humidity of 70%） was relatively fast， and the conversion of non-structural sugars was rapid， resulting in the early yellowing of tobacco leaves.Tobacco leaves under the high humidity （yellowing humidity of 90%） had relatively small changes in various indexes at the early stage of yellowing， but the conversion rate of non-structural sugars after 144 hours was faster， which prolonged the yellowing period to some extent.The degree of degradation and transformation of plastid pigments and non-structural sugars in tobacco leaves under the moderate humidity （yellowing humidity of 80%） was between that under the low humidity and the high humidity.The above results show that the high humidity air-curing provides a more suitable environment and time conditions for the yellowing of tobacco leaves， and promotes the transformation of the substances contained in tobacco leaves.Therefore， in the actual production， providing a high humidity air-curing environment for tobacco leaves during the yellowing period is more conducive to the formation of high-quality tobacco leaves.