Abstract: An experiment was conducted in field to study the effects of nitrogen and phosphorus fertilizer on photosynthetic characteristics of flag leaf in hybrid wheat. The results showed that in the range of application of N 122.5—337.5 (kg/hm2) and P2O5 90—270 (kg/hm2), the net photosynthetic rate (Pn), chlorophyll content (Chl), soluble protein content (Pro), stomatal conductance (gs) and mesophyll conductance(gm) of flag leaf in hybrid wheat were increased with the increasing rates of fertilizers, and the photosynthetic duration prolonged, therefore, the leaf source capacity increased. All the parameters above of the female parent C6-38 were similar to those of hybrid F1, but the male parent Py85-1 were contrary under the treatments of high and middle fertilizer. During the whole senescence period of flag leaf, the average heterosis of net photosynthetic rate and photosynthetic duration of hybrid F1were increased with the increasing rates of fertilizers, and during the late period of senescence were more significant than those during the early and middle periods.