Abstract: The effect of nitrogen source on the growth and development of flue-cured tobacco root system was studied by pot experiment.The results showed that the growth and development of root system could be promoted by equal application of NO₃^--N and NH₄⁺-N at early stage, and the same effect could be obtained with 20% nitrogen of cake fertilizer +40% NO₃^--N +40% NH₄⁺-N at later stage, which led to the enhancement of root activity, the decrease of breath intensity, the increase of root dry matter weight, better downward stretching of root in soil, higher contents of nicotine, soluble total sugar and starch, and vigorous root system.