Abstract: In order to explore the effect of planting density on the carbon and nitrogen metabolism during the growth of cigar leaves, taking Dexue No.1 as test material, the effects of four densities of 19 500 plants/ha (T1), 21 000 plants/ha (T2), 22 500 plants/ha (T3) and 24 000 plants/ha (T4) on key enzyme activities of carbon and nitrogen metabolism, plastid pigments, chemical composition and sensory quality of tobacco leaves were studied. The results showed that T2 and T3 treatments can increase the activities of amylase (AL), neutral invertase (NI), nitrate reductase (NR), and total sugar and starch contents. With the increase of density, the total nitrogen and carotenoid contents decreased and the chlorophyll content increased during the growth of cigar leaves. With the increase of density, the contents of total sugar and reducing sugar, as well as the sugar-nicotine ratio and nitrogen-nicotine ratio increased, but the total nitrogen and nicotine content decreased after air-during. Under the T2 treatment, the contents of starch and protein were the lowest, the potassium-chlorine ratio was higher, the chemical components were suitable and the sensory quality was good. Therefore, the suitable planting density for cigar leaves was determined to be 21 000 plants/ha in Shifang, Sichuan Province, which is conducive to increase the carbon and nitrogen metabolism capacity, improve the quality and availability of cigar leaves.