Abstract: To investigate the effects of harvest maturity on the contents of sugars, alkaloids and aroma substances in cigar tobacco leaves after air-curing, the maturity characteristics of leaves from two cigar tobacco varieties, Haiyan 101 (HY101) and Haiyan 200 (HY200), harvested at 14 days (M1 treatment), 21 days (M2 treatment) and 28 days (M3 treatment) after topping were analyzed. The effects of maturity levels on the contents (mass fractions) of water-soluble sugars, alkaloids and aroma substances after air-curing were also studied. A structural equation model was used to predict the key factors driving the variations in sugars, alkaloids and aroma substances among the cigar tobacco leaves with different harvest maturity levels. The results showed that: 1) As harvest maturity increased, the metabolism level of plastid pigments in fresh leaves decreased significantly, accompanied by an expansion of the yellowing region in the leaves. 2) After air-curing, the sucrose content decreased gradually with increasing harvest maturity, whereas the contents of glucose, fructose and maltose increased gradually. However, the contents of nicotine, neonicotine and anatabine in HY200 leaves did not exhibit significant variations. 3) The analysis results of the orthogonal partial least squares discriminant model indicated that the aroma substance contents in the air-cured cigar tobacco leaves significantly varied at different harvest maturity levels. The contents of carotenoid degradation products and aromatic amino acid degradation products were higher in the M1 treatment, whereas the contents of Maillard reaction products were higher in the M2 and M3 treatments. 4) Structural equation model analysis revealed that the plastid pigment level directly or indirectly influenced the contents of carotenoid degradation products after air-curing and indirectly affected the accumulation of Maillard reaction products by affecting the contents of glucose and maltose. Consequently, higher plastid pigment accumulation in the cigar tobacco leaves harvested 14 days after topping facilitated their complete degradation into carotenoid degradation products during air-curing, enhancing floral and fresh aroma characteristics. In summary, delaying harvest appropriately resulted in lower plastid pigment contents and higher photosynthate accumulation in fresh leaves. During air-curing, sucrose was fully degraded into monosaccharides, furnishing ample substrate for the Maillard reaction and indirectly promoting the accumulation of Maillard reaction products. Therefore, it is recommended that the middle leaves of HY101 and HY200 cigar tobacco varieties in Guangdong tobacco growing area be harvested 21 days after topping.