Abstract: With the increasing water shortage, improving water use efficiency is becoming more and more important. Reducing the transpiration of a plant is a way to reduce crop water use. Experiments were carried out. The effects of defoliation on photosynthesis, dry matter translocation, grain yield and water use efficiency (WUE) were investigated with different defoliation degrees and different soil water levels. The field experimental results show that defoliation enhanced the photosynthetic capacity of the remaining leaves. The defoliation under water deficit conditions advances dry mater translocation from the remaining leaves and the straw to the wheat grain, and the treatments of 30% and 60% defoliation increased more translocation of dry matter to the wheat grain than that of the others. The 30% and 60% defoliation treatments did not affect grain yield of the winter wheat, while the 90% defoliation under deficit conditions significantly reduced crop water use, but resulted in significant decrease of grain yield and reduced WUE. Moderate defoliation under water stress might be beneficial to crop production.