The effects of nitrogen (N) application on maize yield, root distribution, and N metabolism were analyzed under high-density planting by using the maize cultivar Xianyu 335 as material, setting up a conventional density treatment of 6.75×10⁴ plants/ha (D1) and a high-density treatment of 8.25×10⁴ plants/ha (D2), and applying N at five rates (0, 160, 220, 280, and 340 kg N/ha) per density treatment. The results indicated that with the increasing of N application rate, the maize yield showed a trend of increasing and then decreasing. The yield of D2 treatment was significantly higher than that of D1 treatment and the combination of high-density planting and optimized N application (160-220 kg N/ha) increased the yield by 39.1%-51.8% compared to conventional management. The optimized combination of N rates and planting densities increased root length, root length density, root surface area, root volume, specific root length, as well as the activities of glutamate synthase and glutamine synthetase in roots. The two enzyme activities were positively correlated with root growth distribution. In conclusion, an application of 160-220 kg/ha of N at a planting density of 8.25×10⁴ plants/ha is recommended. This combination enhances nitrogen metabolism enzyme activities, promotes root growth, and increases soil nutrient uptake, thereby improving maize yield. This can serve as a high-yield maize planting model for the Guanzhong region of Shaanxi.