Abstract: In order to minimize potential human bias on the evaluation of the maturity and flue-curing quality of fresh tobacco leaves and the grading of greenish tobacco leaves, the yellowing process of fresh tobacco leaves and the difference of spectral characteristics between the normal area and the greenish area of flue-cured tobacco were analyzed based on the hyperspectral imaging technology, and the greenish characteristics of tobacco leaves were quantitatively characterized by using the spectral absorption index (SAI) method. The results showed that: 1) Within the band of 400-780 nm, the spectrum of the greenish area in tobacco leaves had the characteristics of "two valleys and one peak". With the weakening of the greenish level, the depth of the absorption valley gradually decreased, and the valley of the normal area in flue-cured tobacco basically disappeared at about 680 nm after curing. 2) The higher the greenish level, the higher the SAI value. 3) When the SAI threshold range was set to 1.19-1.28, the normal group, slightly green group, greenish-yellow grade 1, and greenish-yellow grade 2 of flue-cured tobacco leaves could be accurately distinguished. 4) By setting different SAI thresholds and combining with color mapping, the location distribution of greenish areas corresponding to different greenish levels in tobacco leaves could be realized. This method provides technical support for the maturity assessment of fresh tobacco leaves, the determination of the yellowing stage progression, and the evaluation of the flue-cured tobacco grade.