Nitrogen( N) is one of the main factors restricting the photosynthesis ,and the deficiency of N will ul-timately affect the yield and quality of crops .Field trials were conducted using Changwu 134 ( Dryland cultivar ) and Zhengmai 9023 ( Irrigated-land cultivar ) as material to study the effect of four nitrogen rates on photosynthesis and biomass of wheat at different growth stages .The results showed that ,in the range of N 0-180 kg/ha,the chlorophyll (Chl)content,photosynthetic rate(Pn),photosynthetic performance index (PI)and biomass of the two varieties at different stages all showed a upward trend with the increasing nitrogen application level .However ,when the nitrogen application level was increased further (≥180 kg/ha),the Pn and biomass of the two varieties began to present a downward trend ,while the PI and Chl contents had no significant changes .Furthermore ,the changing trend of yield with increasing nitrogen level were the same to that of phtosynthesis and biomass in the two varieties , the highest yiled being from the treatment 180 kg/ha.%在大田试验条件下，以长武134（旱地品种）与郑麦9023（水地品种）为试验材料，研究了4个施氮水平对小麦不同生育时期光合作用和产量的影响。结果表明：在0～180 kg/hm2施氮水平范围内，随着施氮量的增加，2个品种的叶绿素（Chl）含量、光合速率（Pn）、光合性能指数（PI）、生物量在各个生育时期均表现为上升趋势；施氮量继续增加（≥180 kg/hm2），2个品种的Pn、生物量开始呈下降趋势，而PI值和Chl含量则无明显变化。同时，随着氮水平的升高，2个品种的产量也表现出先升后降的趋势，在180 kg/hm2施氮水平时小麦产量最高。
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