Abstract: In order to reveal the carbon and nitrogen metabolism in flue-cured tobacco leaves precisely fertilized with nitrogen by SPAD meter at maturity stage, treatments of SPAD-based N-fertilization (SPAD value of 43) and conventional N-fertilization by farmer on cv. K326 were compared. The contents of compounds involved in carbon and nitrogen metabolism and enzyme activities in every other leaf, starting from the second one on tobacco stalk were separately determined at the maturity stages of lower leaves and middle leaves. The results showed that comparing with the leaves fertilized by conventional N-fertilization by farmer, the contents of free amino acid, soluble protein and total nitrogen and the activities of glutamine synthase, nitrate reductase and invertase decreased in the leaves fertilized by SPAD-based N-application, while the contents of total sugar, reducing sugar and amylase activities increased. It indicated that precise nitrogen application based on SPAD meter promoted smooth transition and transformation of carbon and nitrogen metabolism in all those leaves, the timely coordinated transition of carbon and nitrogen metabolism at maturity stage was reflected by decreasing total nitrogens and increasing sugars to the right levels at the right time, the ratio of sugar to nitrogen was more harmonious, and the quality of tobacco leaves improved.