Abstract: The effects of nitrogen (N) levels (as slow-release fertilizer) on yield, dry matter production and leaf area index of summer maize under super- high yield conditions were studied in 2013. A field trial was conducted using two maize hybrids (Suyu29 and Suyu30) as materials under seven N treatments (0, 270, 315, 360, 405, 450, and 495 kg/hm², respectively) by split plot design. The results showed that with the increment of N application amount, the grain yield gradually increased and peaked at N 450 kg/hm² treatment, which were 16193 kg/hm² and 14040 kg/hm² for Suyu29 and Suyu30, respectively, and both varieties reached the marginal product at N 405 kg/hm² treatment. The dry matter accumulation rate and leaf area index of summer maize under super-high yield treatments was higher at the early grain filling stage, and both parameters decreased slowly with the proceeding of grain filling. The analysis results of Richards equation model indicated that under the super-high yield conditions, the days with higher dry matter accumulation rate prolonged 10 days, and more days resulting in higher yield. Compared with the blank, the active growth period extended 9 days and the maximal accumulation rate of dry materials increased 43.5% under higher yield conditions. In conclusion, moderate N applications (405 kg/hm²) reduced the rate of the leaf area index and the decreasing rate of dry materials accumulation, prolonged the date with maximal dry matters accumulation rate and the active growth period, which led to the higher grain yield.