Abstract:Photosynthesis and transpiration of flag leaf of winter wheat in Feng-qiu Agricultural Experiment station of CAS were measured at different growing stages with model Li-6400 photosynthesis system. In addition, variables such as the leaf temperature, photosynthesis active radiation, relative humidity, stomatal conductance, intercellular CO2 concentration were also measured. This experiment studied the relations between the net photosynthesis rate & transpiration rate of flag leaf and ecological & physiological factors. The results showed that Pn of flag leaf rose when PAR increased, the light compensation point of photosynthesis (Ic) and light saturation point of photosynthesis (Isat) in flag leaves were respectively about 50-60 μmol•m-2 •s–1 and 1050-1100 μmol•m- 2 •s -1; Tr of flag leaf showed a positive linear correlation with PAR. The relative coefficient between Ta and Tl was 0.886**, Pn of flag leaf rose as Ta and Tl increased, then began to decrease when Ta and Tl exceeded 30 ℃ and 32 ℃ respectively; Trof flag leaf showed a positive linear correlation with Ta and Tl. Relative coefficient between Pnand Gs was r=0.407**, relative coefficient between Tr and Gs was r=0.322**; both first rose while Gs increased, then decreased when Gs exceeded 0.2 mol m- 2 s -1. Pn and Tr decreased when Ci increased. PAR and Gs were the dominant factors affecting plant photosynthesis and transpiration.