In order to clarify the characteristics of photosynthesis and yield responses of summer maize to pre-sowing irrigation advancement for winter wheat, a single factor experiment of irrigation times (Sep. 30th, Sep. 25th, Sep. 20th written as I9.30, I9.25, I9.20) was conducted during 2011—2012 and no irrigation advancement treatment was taken as control (CK). The results indicated that the diurnal variation of net photosynthesis (Pn) in ear leaf of maize was different among the four treatments, CK showed a single peak curve, while the other three treatments showed bimodality. As to the averages of the diurnal variation of Pn of each treatment, I9.20 and I9.25 were higher than others and the change of leaf source capacity (LSC) of the total three near ear leaves appeared a similar pattern, i.e., I9.20 and I9.25 showed higher values. The changing of sugar content in maize stem, however, was different from that of the photosynthesis characteristics; the stem sugar content of CK was higher than those of other treatments. Grain filling was also influenced by different irrigation treatments. The I9.20 and I9.25 treatments showed larger maximum filling rates, longer active grain filling periods, and higher grain weights and grain yield. Different irrigation times had effect on the dry matter distribution as well. The amount of accumulated dry matter after anthesis of different treatments showed a trend as I9.25>I9.20>I9.30≥CK, which demonstrated that the pre-sowing irrigation advancement of winter wheat was able to improve the population photosynthetic performance, promote dry matter translocation from vegetative organs to grains after anthesis, and finally increase the grain yield of maize in Hebei Plain. The best period for irrigation advancement in this experiment was from Sep. 20th to Sep. 25th.