To investigate the characteristics of the dynamic changes of root morphology of silage maize in different periods under the conditions of nitrogen and phosphorus rationing in the wind and sand area of Yulin, silage maize (Zea mays) ‘Dajingjiu 23’ was used as the research object. A two-factor test was set up for nitrogen and phosphorus fertilizers, with the nitrogen application of no nitrogen (N0, 0 kg/hm²), low nitrogen (N90, 90 kg/hm²), medium nitrogen (N180, 180 kg/hm²), medium-high nitrogen (N270, 270 kg/hm²) and high nitrogen (N360, 360 kg/hm²); and phosphorus was applied as no phosphorus (P0, 0 kg/hm²), low phosphorus (P90, 90 kg/hm²) and high phosphorus (P180, 180 kg/hm²). The biomass and root morphology of silage maize were measured at the trumpet stage, silking stage and harvesting stage. The results showed that the nitrogen-phosphorus rationing significantly promoted the longitudinal development of the root system at the trumpet stage, and the fresh weight, root length and surface area of the root system in the 10-20 cm soil layer increased by 73.9%-169.5%, 52.0%-136.4% and 75.1%-124.4%, respectively. Nitrogen-phosphorus rationing had a significant effect on the expansion of the shallow root system during the silking stage, with the fresh weight, dry weight and volume of the root system in the 0-10 cm soil layer increasing by 5.5%-69.3%, 3.9%-62.1% and 3.0%-91.4%, respectively. Nitrogen-phosphorus rationing effectively delayed root senescence at harvest, with increases of 28.5%-190.3% in fresh weight in the 10-20 cm soil layer, and increases of 50.0%-202.3% and 40.2%-158.8% in dry weight and volume in the 20-30 cm soil layer, respectively. The root indexes of each fertility stage showed that the fresh weight, dry weight, root length, surface area and volume of roots in the 0-20 cm soil layer were significantly better than those in the 20-40 cm layer. Through the comprehensive evaluation of the affiliation function, the optimal performance of the N180P180 program was observed, with the above-ground fresh and dry weights increasing by 24.7% and 44.7%, respectively, and the root development indexes showing a sustained gain. The fresh weights increased by 54.5%-91.1%, the dry weight increased by 28.5%-70.6%, the root length increased by 23.8%-70.8%, the total area increased by 52.1%-79.3%, and the total volume increased by 32.6%-98.9%, and a significant increase in the efficiency of nutrient uptake by the plant. In conclusion, the N180P180 dosage was favorable to promote the synergistic growth of maize above-ground and below-ground.