Abstract: A field experiment was conducted in Wuqiao Experimental Station of China Agricultural University in 2011. Four nitrogen (N) application patterns were compared: N application rate of 90 kg·hm^-2 before sowing (NAT I); N application rate of 190 kg·hm^-2 with 150 kg·hm^-2 before sowing and 40 kg·hm^-2 at jointing (NAT II); N application rate of 250 kg·hm^-2 with 90 kg·hm^-2 before sowing and 160 kg·hm^-2 at jointing (NAT III); and N application rate of 300 kg·hm^-2 with 50 kg·hm^-2 before sowing, 150 kg·hm^-2 at jointing and 100 kg·hm^-2 at silking (NAT IV). The objective of the study was to throw in-depth light on how the mechanisms of N application at silking stage in addition to basal and jointing N fertilization increase summer maize yield. Yield and grain-filling rates of summer maize were also analyzed. The results showed that N application at silking stage in addition to basal and jointing N fertilization (NAT IV) reduced the number of dead leaves. Leaf senesces rates were 0.01~0.02 leaf·d^-1, 0.01~0.05 leaf·d^-1, 0.02~0.04 leaf·d^-1, respectively, less than those of N treatments without silking N fertilization at 11~20 d, 21~30 d, 31~40 d after silking. Ear leaf SPAD peak value was somewhat higher in NAT IV than that of other treatments, and the reduction of SPAD at middle and later filling stage was delayed. Furthermore, peak of NAT IV filling rate improved by 8.5% over that of NAT Ⅲ and with simultaneous increase in grain volume. Maize grain N uptake after silking significantly improved in NAT IV (grain nitrogen absorption peak in NAT IV was 1.65, 1.45 and 1.31 times than those of NAT Ⅰ, NATⅡ and NAT Ⅲ, respectively). N harvest index was 2.5%~13.3% greater in NAT IV than in the other treatments. Compared to kernel per ear, grain weight was more affected by N application at silking stage. Both ear traits and yield formation were improved under NAT IV, and yield increased by 200 kg·hm^-2, 300 kg·hm^-2 and 400 kg·hm^-2, respectively compared with NAT I, II, III. It was concluded that silking fertilization in summer maize delayed decreasing of photosynthetic area after silking. This provided more grain filling source that in turn improved grain weight and yield.