The way of one-time basic fertilizer application causes imbalance of nutrients supplies in the whole growth period of crops, which results in the deficiency of nutrients and premature senility in the late growth period. In order to investigate the mechanism of polyaspartic acid-chitosan (PAC) in soil nitrogen supply and regulation of antioxidant properties in foxtail millet leaf after flowering in the northeast China and establish an anti-aging and high-yielding technology under the background of one-time basic fertilizer application, a field experiment was conducted using foxtail millet (Setaria italica) varieties of Zhangzagu 13 and Huayougu 9 in Gongzhuling Experimental Station of Institute of Crop Sciences (Chinese Academy of Agricultural Sciences) from 2020 to 2021. Conventional fertilization (CN) and PAC with fertilization (PN) treatments were set under six nitrogen levels of 0, 75, 112.5, 150, 225, and 337.5 kg·hm^-2 with all fertilizer applicated before sowing. Our results showed that, compared with CN under the same nitrogen application level, PAC increased NO₃^--N and NH₄⁺-N content in the 0-20 cm and 20-40 cm soil layers of two foxtail millet varieties at anthesis and mid-filling stage. Meanwhile, PAC increased leaf area and decreased leaf area reduction per plant significantly. The activities of superoxide dismutase, peroxidase and catalase of the flag leaf increased but the content of malondialdehyde reduced in 0-40 days after flowering. Thus, PAC ensures the supply of nitrogen in soil during the middle-late growth period, increases the antioxidant properties of leaf to delay the progress of leaf senescence and increase yield of foxtail millet effectively. In 2020 and 2021, the yield of Zhangzagu 13 increased by 11.24%-21.55% and 8.65%-14.22%, respectively, and the yield of Huayougu 9 increased by 5.53%-15.75% and 10.43%-16.17%, respectively, compared with CN under the same nitrogen application level. The effect of the items above was more significant at low-middle nitrogen application levels of 75, 112.5 and 150 kg·hm^-2. Therefore, PAC combined with nitrogen fertilizer could be an anti-aging and high-yielding cultivation technique in foxtail millet production in the northeast China spring-sowing region.