Abstract: Results of pot experiments showed that even slightly water deficit from jointing to flowering stage reduced winter wheat yield, while no yield reduction was found when mild water stress was imposed at turning green stage and milky stage. At different level of water deficit, the yield sensitive index (or coefficient) to water stress varies. After winter wheat undergoes a short term of water stress and when water supply resumed, its growing speed will increase, which is the compensatory growth effect. Then yield reduction is smaller compared with the decreasing in evapotranspiration. The stomatal conductivity and leaf water potential of winter wheat decrease with the decreasing of soil water content when soil moisture is lower than 60% of field capacity, otherwise they don't change very much when it was over 60%.

Key words: Water deficit, Development stage, Winter wheat