Objective] To research the effects of nitrogen application level on the antioxidant defense system and quality of flue-cured tobacco leaves.[ Method] Taking K326 as experimental materials,we researched the effects of different nitrogen application levels on active oxygen con-tent,SOD activity,GR activity,APX activity,antioxidants content and chemical components in tobacco leaves.[Result] With the growth and rip-ening of tobacco leaves in fields,generation rate of O2 -· and content of hydrogen peroxide of tobacco leaves presented increasing trend .Activi-ties of SOD,GR and APX increased firstly,and then decreased.Content of AsA increased at early growth stage and decreased gradually at late growth stage.Nitrogen application level had significant effects on antioxidant defense system.The contents of free radical scavenger (GSH,AsA) and activity of related enzymes (SOD,GR,APX) of antioxidant defense system at high nitrogen level were significantly or extremely significantly higher than those at low nitrogen level.With the increasing of nitrogen application level,the contents of nitrogen compounds of cured tobacco leaves increased significantly,while degradation amount of macro molecular substance decreased ,such as protein,starch,chlorophyll and carote-noid,and the content of petroleum ether extract also reduced.However,it showed no significant impacts on potassium and chlorine.Thus,the quality of tobacco leaves reduced.[ Conclusion] In field management of flue-cured tobacco,rational application of nitrogen fertilizer (45.0 kg/hm2 ) is beneficial to keep the higher activity of antioxidant defense system to resist stress at early growth stage ,mature timely at mature peri-od,and improve the quality of tobacco leaves.%[目的]研究施氮量对烤烟烟叶抗氧化系统及质量的影响。[方法]以K326为试验材料，对不同施氮水平烤烟生长成熟期间烟叶活性氧含量、SOD活性、GR活性、APX活性、抗氧化剂含量、化学成分进行了研究。[结果]随着烟叶在田间的生长成熟，烟叶内超氧阴离子产生速率、过氧化氢的含量呈增加趋势；抗氧化酶活性整体呈先上升后下降的趋势；抗氧化剂GSH逐渐下降；AsA含量在生长前期逐渐增加，但生长后期逐渐下降。不同施氮水平对烤烟烟叶生长成熟期间抗氧化系统有显著影响。在高氮水平下，烟叶内活性氧清除系统中的自由基清除剂（GSH、AsA）和相关酶活性（SOD、GR、APX）均显著或极显著高于低氮水平处理。随着施氮量的增加，烤后烟叶含氮化合物显著增高，蛋白质、淀粉、叶绿素和类胡萝卜素等大分子物质降解量减少，石油醚提取物显著减少，但对钾和氯影响不显著，烟叶质量降低。[结论]烤烟大田管理中适量施氮（45．0 kg／hm2）有利于烟叶生长前期保持较高抗氧化活性，抵御胁迫，在成熟期确保适时成熟，提高烟叶质量。
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