Field experiments were conducted in the test station of Dry-land Farming Institute of Hebei Academy of Agricultural and Forestry Sciences during 2011—2012. Three summer maize cultivars, Xundan 20, Zhengdan 958 and Xianyu 335, were used as experimental materials. The measurements were taken on irrigation by three stages (Sep.20, Sep.25, Sep.30). The main results showed that compared with CK, different irrigation treatments during late milk period had increased the soil moisture by 2.92%~14.14% in 0~100cm layer at harvest. The evapotranspiration amounts of maize were ranged within 380.67~434.91mm, and different treatments from small to large were I9 25, I920, I930 and CK. Different treatments also had effects on the dry matter distribution. The treatments of CK and I930 increased amount of assimilate storage in vegetative parts before silking to grains. I920 and I925 treatments, however, increased amount of assimilate storage in vegetative after silking to grains. Grain yield of I920 and I925 treatments were higher than those of other treatments. Water use efficiency for grain yield was range within 21.94~26.53kg/m3, water use efficiency for grain yield of I925, I 920 and I930 treatments were most obviously lower than that by CK treatment. This shows that at optimum irrigation time after milking, grain yield increases although water use efficiency for grain yield decreases. In comprehensive consideration of cultivating technique of high yield and efficiency for unified wheat and maize, the best time for irrigation was on 20~25 September.