The model couples stomatal conductance (gs) and net photosynthetic rate (PN) describing not only part of the curve up to and including saturation irradiance (Imax), but also the range above the saturation irradiance. Maximum stomatal conductance (gsmax) and Imax can be calculated by the coupled model. For winter wheat (Triticum aestivum) the fitted results showed that maximum PN (Pmax) at 600 μmol mol−1 was more than at 350 μmol mol−1 under the same leaf temperature, which can not be explained by the stomatal closure at high CO2 concentration because gsmax at 600 μmol mol−1 was less than at 350 μmol mol−1. The irradiance-response curves for winter wheat had similar tendency, e.g. at 25 °C and 350 μmol mol−1 both PN and gs almost synchronously reached the maximum values at about 1 600 μmol m−2 s−1. At 25 °C and 600 μmol mol−1 the Imax corresponding to Pmax and gsmax was 2 080 and 1 575 μmol m−2 s−1, respectively.