Abstract: Taking the high-yielding summer maize cultivars Denghai 661 (DH661) and Zhengdan 958 (ZD958) as test materials, a field experiment was conducted to study their grain yield, nitrogen use efficiency, key enzymes activities of nitrogen metabolism, and antioxidant enzymes activities under effects of different nitrogen application periods. One-dose nitrogen application at jointing stage was not beneficial to the increase of grain yield and the nitrogen accumulation in plant and grain, while split application in combination with application after anthesis increased the nitrogen accumulation in plant and grain significantly and increased the grain yield. When the nitrogen was applied at a ratio of 2：4：4 at jointing stage, 10-leaf stage, and 10 days after anthesis, the grain yield of DH661 was up to 14123.0 kg·hm^-2; when the nitrogen was applied at a ratio of 1：2：5：2 as the basal and at jointing stage, 10-leaf stage, and 10 days after anthesis, the grain yield of ZD958 was up to 14517.1 kg·hm^-2. These two nitrogen application modes increased the grain yield of DH661 and ZD958 by 14.5% and 17.5%, respectively, as compared with onedose nitrogen application at jointing stage. Split nitrogen application before anthesis increased plant nitrate reductase  activity significantly. In the 0-42 days after anthesis under split nitrogen application, the glutamine synthetase, glutamate synthase, and glutamate dehydrogenase  activities of DH661 and ZD958 were averagely increased by 32.6%, 47.1% and 50.4%, and 14.5%, 61.8% and 25.6%, and the superoxide dismutase  and catalase activities were increased by 22.0% and 36.6%, and 13.4% and 62.0%, respectively, and the malondialdehyde content was decreased significantly, as compared with oneoff nitrogen application. It was suggested that for the high-yielding of summer maize, split application of nitrogen and appropriately increasing the nitrogen application ratio after anthesis could enhance the plant key nitrogen metabolism enzymes activities, delay leaf senescence, promote plant nitrogen uptake and its utilization, and increase grain yield.