| The experiment was conducted under drought condition (water withholding) to investigate the photosynthetic parameters in flag leaves of the high-yield wheat (Triticum aestivum L.) varieties Ningmai 9, using Ningmai 8 as control. The results showed that in the course of water withholding, there were constant decreases in relative water content of soil (RWCS), leaf relative water content (RWCL), net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E), and mesophyll conductance (gm, calculated as the ratio of Pn to Ci). During 08 d of water withholding, subcelluar CO2 concentration (Ci) decreased and water use effiCiency (WUE) increased, whereas during 812 d of water withholding, Ci increased and WUE decreased significantly. There was a close positive correlation between Pn and gm (R2=(0.938,) P<0.0001), but no clear correlation between Pnand gs was observed. It could be concluded that under both mild and serious drought conditions, non-stomatal limitation may be the primary factor to inhibit photosynthesis, rather than stomatal conductance. Compared with Ningmai 8, Ningmai 9 had a higher Pn, gs, gm and WUE, and a lower E. Moreover, drought induced a slower decrease in Pn in Ningmai 9 than in Ningmai 8, indicating a stronger drought-resistance in the former. Therefore, the properties of high photosynthetic capacity, WUE and drought-resistance may be the physiological basis of high-yield in Ningmai 9, whose drought-resistance could be attributed to the high water use efficiency. |