Abstract: Nitrogen (N) is an important prerequisite for achieving high grain yield of summer maize. The objective of this study was to reveal the responses of summer maize to N levels in the morphology characteristics of plants and the yield component factors in some super-high yield (13500 kg/ha) maize cultivars. A field experiment with a split-plot design was conducted with three local maize hybrids (Suyu30, Suyu20 and Suyu29) and six N fertilizer application rates (0, 360, 405, 450, 495 and 540 kg/ha). The statistics results show that a parabolic relationship existed between the yields of three maize hybrids and N rates. The maximum yields turned up at the N 450 kg/ha level, which are 13798, 14531 and 16787 kg/ha, respectively. The kernel weight per ear, grain length, grain width and the length of internode near ear are increased markedly under the N 450 kg/ha, which are 239 g (take Suyu29 for example), 12.29 mm, 10.83 mm, 20.2(above), 43.3(middle) and 26.1(below), respectively. The lengths of 1st, 2nd and 3rd internodes and stem diameter are also increased, which are 11.1, 11.4, 11.4 and 2.35 cm, respectively, while the lengths of internodes near ear (7th, 8th and 9th internodes) are decreased, which are 14.3, 14.0 and 15.5 cm, respectively. The N level does not have insignificant effect on the grain thickness. The yield and stem diameter show significant or extreme significant positive correlations with the lengths of 1st, 2nd and 3rd internodes, but significant negative with the length of 7th internode, and not insignificant with the other lengths of internodes. Therefore, big grain length and width can be used as indicators in breeding super high-yield of maize cultivars. In practical maize production, proper N application can be used effectively to regulate the lengths of 1st, 2nd, 3rd and 7th internodes, thus to build up the super high-yield population of maize through enlarged N sink and effective transfer to yield formation.