Abstract: The effects of soil water deficit in different stages of reporductive growth on the photosythetic organs, photosynthetic rate and photosynthetic products of faba bean (Vicia faba), cultivar Xichang Dabai were investigated in a pot experiment. The experiment was conducted with six treatments of irrigation (Control) and drought at bud to initial bloom, initial bloom to full bloom, full bloom to initial pod, initial pod to full pod and full pod to plump pod stage.The results indicated that total photosynthesis, net photosynthesis. Chlorophyll content, leaf area, stomatal width, biomass and grain yield were decreased by all the soil drought treatments, but stomatal density and respiratory rate were increased. The light saturation point of droughty leaves was decreased from 50kLx to 30kLx, and the stomatal open of droughty leaves was 9--10 hour. The plant response at different growth stages to soil drought treatment was different. The plant of soil drought at the bud appearance to initial bloom stage was less affected, but the plant at initial pod to full pod stage was most sensitive to soil drought treatment. When the faba bean was dried at the stage, the biomass and grain yield per plant were reduced by 32.0% and 44.9%, respectively. The decreased level of the photosynthetic characteristic at different growth stages by soil drought treatment agrees with the level of biomass and grain yield. These results suggest that the initial pod to full pod stage is the critical moisture point of faba bean.