Abstract: The studies on flue-curing process shows that the nitrate, nitrite and N-TSNAs content increased in the period of yellowing, decreased in the period of color-fixing, and changed a little in the period of stem drying; These contents are definitely higher after flue- curing. The content of MDA, relative electrical conduct and extent of injury in tobacco leaves increase sharply in the period of yellowing, and then increase slowly in the period of color-fixing and stem drying till the end of flue-curing.