Abstract: By using the method of apoplast extraction and determination of enzymes related nitrogen metabolism, the influence of Glufosinate (GS) inhibitor concentrations on nitrogen metabolism physiological indices of flue-cured tobacco varieties with two nitrogen use efficiency were studied. The results show that GS inhibitors could inhibit GS activity of tobacco leaf during senescence, reduce the ability of nitrogen assimilation, promote the degradation of nitrogen nutrient, induct the increasing of glutamate dehydrogenase (GDH) activity and decreasing of nitrate reductase (NR) activity and promote accumulation of leaf NH₄⁺, increase ammonia volatilization potential. These inhibition effects became more obvious with increasing GS inhibitor concentration. Compared with high nitrogen efficiency varieties, low nitrogen efficiency varieties aged more rapidly and had a lower NH₄⁺ accumulation and ammonia volatilization potential. There was significant difference between varieties. This shows that GS inhibitors can accelerate leaf senescence and promote nitrogen degradation and transfer.