Abstract: By examining the related indices of flue-cured tobacco curing properties, we studied the effect of topping time on the curing characteristics and the difference among varieties. The results showed that delaying topping could promote degradation of leaf chlorophyll and carotenoid before curing and during the process of curing, and decrease leaf moisture and increase water loss rate, increase malondialdehyde content and decrease polyphenol oxidase activity, and increase the proportion of yellow leaves after curing. If topping was too late, tobacco plastid pigment content was too low, water loss and aging speed were too fast, thus causing imbalance of yellowing or black leave. Difference among variety was important factors which influenced curing characteristics and topping time.