Abstract: The results indicated that nitrogen nutrition supplied at flag leaf initiation could increase the chlorophyll content and photosynthetic rate, delay the senescence and photosynthetic decline of leaf during leaf aging process. At the meantime, nitrogen nutrition made the leaf cytokinin(ZRs) content increase and abscisic acid(ABA) content decrease. Duing leaf aging process, nitrogen treatment could also increase the RuBPcase activity, PS1 and PS2 activity, but the increase of RuBPcase activity was much higher than that of PS1 and PS2 activity. Which relatively increased the rations of RaBPcase activity to PS1 activity and PS2 activity, and improved the balance state between the light reaction and dark reaction of photosynthetic organ. The suplus photosynthetic reductivity produced by light reaction was little. Otherwise, compared with CK, nitrogen nutrition decreased the O2 Producing rate and the accumulation amount of H2O2 in leaf, and increased the enzymatic activity of active scavenging enzyme SOD and CAT during leaf aging process. It is suggested that nitrogen nutrition probably is mainly by regulating the hormone balance in the leaf cell, and improving the cycling metabolism of the photosynthetic organ. to decline the producing rate and accumulation amount of active oxygen in the leaf, and inhance the activity of active oxygen scavenging enzyems. Which is one important physiological factor that the leaf senescence and the photosynthetic function decline can be delayed regulated by nitrogen nutrition.