Abstract:A field trial on the wheat root activity, chlorophyll content and photosynthetic rate showed that the decline of root activity was earlier and faster than that of flag leaf chlorophyll content and photosynthetic rate, and there was a positive correlation between root activity and leaf photosynthetic rate(r=0.8006).Topdressing nitrogen fertilizer at elongation stage could obviously improve root activity and photosynthetic rate, decrease leaf ABA con-tent, increase ZRs content and SOD activity, and delay the peak value of MDA for 8～10 days, which suggested that the variation of root activity was closely related to the senescence of flag leaf. Improving root nutrition and root activity at earlier growth stages could delay the senescence of wheatleaf.