Chlorophyll fluorescence could be used as an index for evaluation of stress tolerance in plants. A field experiment was conducted using 3 wheat varieties along with seven irrigation levels in a factorial arrangement of a randomized complete block design with four replications. Chlorophyll fluorescence parameters were measured on plant flag leaves about 3 weeks after anthesis. Variations of maximum chlorophyll fluorescence (FM), fluorescence variable (FV), minimum chlorophyll fluorescence (F0),half time of increase from F0 to FM (T1/2) and the photochemical capacity of photo-system II (FV/FM), were evaluated. Relative water content and flag leaf chlorophyll content were measured. Results showed that different irrigation levels affect FV, FV/FM and T1/2 significantly(P £0.05).Both factors of cultivars, and different irrigation levels affected chlorophyll content, RWC and grain yield (GY) significantly (p£0.01). Mean FV/FM, FV, T1/2 and FM declined as soil water content was decreased, but F0 almost remained constant for all the treatments. High yielding varieties exhibited higher values for TI/2, FM, FV/FM, FV, chlorophyll content and RWC. The highest correlation coefficient was observed between grain yield and FV as well as FV/FM, while the lowest detected between grain yield and F0.The existence of similar patterns of variation in fluorescence parameters in all varieties indicates that high yielding varieties can overcome the effects of drought stress during grain filling period, this being confirmed by correlation between fluorescence parameters and RWC.