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 P_n 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; T_r of flag leaf showed a positive linear correlation with PAR. The relative coefficient between T_a and T_l was 0.886**, P_n of flag leaf rose as T_a and T_l increased, then began to decrease when T_a and T_l exceeded 30 ℃ and 32 ℃ respectively; T_r of flag leaf showed a positive linear correlation with T_a and T_l. Relative coefficient between P_nand Gs was r=0.407**, relative coefficient between T_r and Gs was r=0.322**; both first rose while Gs increased, then decreased when Gs exceeded 0.2 mol m- 2 s -1. P_n and T_r decreased when Ci increased. PAR and Gs were the dominant factors affecting plant photosynthesis and transpiration.