Abstract: The field plot experiments on effects of the proportion of NO₃^--N to NH₄⁺-N on agronomic characteristics, chemical components, yield and quality of flue-cured tobacco planted in clay loam soil of middle fertility was conducted from 2000 to 2001.The results showed that when nitrogen application rate was 45 kg/ha with the proportion of 75% NO₃^--N to 25% NH₄⁺-N, the cured leaves had relatively higher potassium and reducing sugar contents, appropriate proportion of main chemical components related to flue-cured tobacco quality, the best economic indexes in terms of yield value and ratio of high and middle grades tobacco leaves.