Abstract: The field experiments of spraying different enzyme modulators were carried out to enhance nitrogen metabolism during the fast growth stage with the purpose of solving the tobacco maturity problem in Dali area. To this end, activities of the key enzymes in nitrogen metabolism and chemical components of flue-cured tobacco were measured. The results showed that spraying ammonium molybdate could increase nitrogen metabolism and the basic materials in the formation of high quality tobacco. Seven days after spraying ammonium molybdate at the rapid growth stage, nitrate reductase (NR) activity, glutamine synthetase(GS) activity and protein content increased by 6.56%, 22.17%, 6.00% and 17.57%, 15.24%, 5.02% in middle and upper leaves, respectively. After spraying sodium tungstate and glufosinate at the maturity stage, nitrogen metabolism had been weakened with nitrate reductase (NR) activity and glutamine synthetase (GS) activity decreased by 8.55%, 18.55% and 5.33%, 11.58% in middle and upper leaves, respectively. Total nitrogen content, nicotine content, protein content decreased, while reducing sugar/nicotine ratio increased. The methods of spraying ammonium molybdate during the fast growth stage and spraying glufosinate during the mature period were effective in regulating nitrogen metabolism and chemical components of tobacco.