Abstract: Three doses of nitrogen ion, 1×10¹⁷ N⁺/cm², 2×10¹⁷ N⁺/cm², and 3×10¹⁷ N⁺/cm², were injected into dry seeds of tobacco cv. RG 17, and 2×10¹⁷ N⁺/cm² was injected into dry seeds of tobacco cv. Yunyan 85. The treated seeds were sowed, the physiological index of tobacco seedling was determined. The results showed that with nitrogen ion injection, the vigor of seedling root system and the content of proline in tobacco leaves were promoted evidently, but the activity of nitrate reductase (NR) was decreased in some degree, the activity of SOD and content of chlorophyll were also improved. The effects of nitrogen ion injection on physiological characteristics varied with different doses and varieties.