Abstract: Modulated chlorophyll fluorescence induction kinetics was used to investigate the effects of altered water conditions on the photosynthetic functions of flag leaves of different winter wheat varieties. The photosynthetic functions include many chlorophyll luorescence parameters such as minimal fluorescence(Fo), maximal fluorescence (Fm) and the ratio of the variable fluorescence to maximal fluorescence Fv/Fm, the potential activities of PSⅡ(Fv/Fo)，photochemical quenching (qP) and non-photochemical quenching (qNP). The results show that Fo and qNP increase, but Fv, Fm, Fv/Fm,Fv/Fo, qP, ETR reduce under the water stress. However, the result is contrary under the altered water onditions.It indicates that PS Ⅱ　reaction center is destroyed by drought stress. When water is supplied at the jointing stage and grain-filling stage, or drought is supplied at two stages but water is supplied at other stages, qP is increased being helpful to enhance the open ratio of PS Ⅱ reaction center and making more photosynthetic energy to be used in the photosynthetic electron transport in order to improve the electron transport capacity. Meanwhile, the increase of non-photochemical quenching coefficient is helpful for the dissipation of excess light energy protecting the photosynthetic tissue and mitigating the stress of environment on photosynthesis.