Abstract: Effect of different N source on physiological characteristics of oriental tobacco were studied in pot. The results showed that the change of invertase activity took on one-peck curve, its peak value appeared at about 65 days after transplant.The change of model metabolism was similar to the change of photosynthetic capacity and N metabolism.Peak value of NR activity appeared at about 50 days after transplant.The total free amino acid contents in tobacco leaf were took on the trend of higher in early phase and lower in rapid growth phase, and then decreased during later mature stage.The C metabolism capacity of upper leaf was higher than that of cutters.The metabolism balance was influenced by different N sources in tobacco growth and the blended N sources of 75% organic and 25% inorganic fertilizer was in favor of C metabolism.