The experiment was conducted to study the effects of regulated deficit irrigation on these parameters of the Korla fragrant pear tree.The water deficit applied before the fruit enlargement stage included: slight water deficit, the trees were irrigated with 60% of US Class A pan evaporation (Ep); severe water deficit, the trees were irrigated with 40% of Ep. During the fruit enlargement stage, both water deficit treatments were irrigated with 80% of Ep. The control was irrigated with 80% of Ep during the whole growth season. The results indicated that the leaf photosynthesis rate, transpiration rate and stomatal conductance were significantly reduced by the soil water deficit. After full irrigation resumed, the leaf photosynthesis rate, transpiration rate and stomatal conductance restored rapidly to some extent, the physiological parameters of slight water deficit reached the control level in the middle August, however, those of the severe water deficit were always lower than the control. As compared with the photosynthesis, the transpiration was more sensitive to the soil water deficit, resulting in the improvement of the leaf water use efficiency.