Abstract: In agroforestry system, trees and crops can make the best use of resources, such as water, nutrient, irradiance and so on. However, competition, particularly the water competition, may occur when the species configuration is not appropriate. The water use of 2-, 6-, and 15-year-old poplar-wheat intercropping systems at four growth period of winter wheat in Yudong Plain area of He'nan Province was studied by using stable carbon isotope technique. The water use efficiency (WUE) and water use quantity (WU) were calculated by using the stable carbon isotope ratio (δ13C), biomass and meteorological data. The results showed that the δ13C and WUE of both poplar and wheat from all the systems showed the highest values at the jointing stages of wheat. Two-year-old poplar had the highest δ13C and WUE values among the three intercropping systems during the whole wheat growth period (except the jointing stage). The δ13C and WUE of wheat from 2-year-old poplar-wheat intercropping was the highest among all the four systems at the seedling establishment stages, while that of sole wheat were the highest during the following growth periods in jointing, flowering-filling and maturing. The water use of sole wheat was 25.71% less than that of 2-year-old poplar intercropped with wheat, but was 2.78 and 1.88 times that of 6-year-old and 15-year-old poplar intercropped with wheat, respectively. The WUE and WU of wheat in all the three intercropping systems generally exhibited higher values at the middle and west of the tree rows than at the east. The wheat height, leaf mass per area, grain yield, total biomass, water use quantity and land equivalent ratio of 2-year-old poplar intercropped with wheat were higher than both sole wheat and wheat from the other two intercropping systems. However, the weight per thousand grain, harvest index and yield water use efficiency of sole wheat was the highest. The above results showed that 2-year-old poplar-wheat intercropping system had the greatest yield and highest land use efficiency. However, with the growing up of poplar trees, wheat is not appropriate to grow under the poplar, and some shade tolerant crop can be planted instead.