Abstract: Effects of drought stress on chlorophyll fluorescence of winter wheat show that T_l/2 the time in ms from the point of variable fluorescence(F_o)to the polnt on the rising curve corresponding to half maximal fluorescence(F_v),F_v／F_m (the ratio of the variable to maximal fluorescence)，F_v/Fo(the ratio of the variable to minimal fluorescence)，and F₁(steady fluorescence)under drought stress condition are evidently lower than those under non-water stres condition．The capacity of PQ store of photosystem II is condensed，and the efficiency of primary light energy conversion of photosystem lI and the potential activities of PS II decrease under drought stress condition．This implies the inhibition of hotosynthetic electron transportation and carbon asimilation under drought stress．