Abstract: The objective of this study was to determine how sowing depth and planting density jointly regulated early growth, root development, tuber spatial distribution, yield formation, and suitable planting combinations of Cyperus esculentus L. in sandy soil in Ejin Horo Banner, Ordos, China. A field split-plot experiment was conducted from May to October 2025 using the cultivar Zhongyousha No. 1. Sowing depths of 5, 7, and 9 cm were assigned to the main plots, and planting densities of 89,000, 105,000, 120,000, 135,000, 150,000, 167,000, and 180,000 hills per hectare were assigned to the subplots, with two tubers sown per hill. Plant growth rate was measured during tillering. Root length, root surface area, root diameter, root dry mass, and root-to-shoot ratio were determined at tillering, tuber formation, and maturity. Tuber numbers in the 0–5, 5–10, and 10–15 cm soil layers were quantified by field profile excavation and sixteen-slice computed tomography. Yield and its components were measured at harvest. Sowing depth, planting density, and their interaction significantly affected most root traits, tuber distribution indices, yield, tuber number per plant, and thousand-tuber mass. During tillering, growth rate generally decreased as sowing depth increased, whereas an appropriate increase in density accelerated early growth. The highest growth rate occurred at a sowing depth of 5 cm and a density of 150,000 hills per hectare, and it was 19.8% greater than that at 89,000 hills per hectare under the same depth. Root development showed distinct responses to depth. Root length and root dry mass were generally greatest at 7 cm, root surface area was greatest at 9 cm, and root diameter was greatest at 7 cm. At the tuber formation stage, 7 cm combined with 167,000 hills per hectare increased root length and root dry mass by 62.5% and 17.0%, respectively, compared with the lowest density at the same depth. At maturity, the same combination increased root diameter by 21.8%. The combination of 9 cm and 167,000 hills per hectare increased root surface area by 23.6% at the tuber formation stage. Tuber number declined progressively with soil depth. Most tubers were concentrated within 0–10 cm, and the distribution pattern obtained by computed tomography agreed with field excavation. A sowing depth of 9 cm combined with 167,000 hills per hectare produced the largest tuber numbers in the upper two layers. Yield increased as density rose from 89,000 to 150,000 or 167,000 hills per hectare, but declined at 180,000 hills per hectare, indicating intensified competition at excessive density. The highest measured yield, 8,351.12 kg per hectare, was obtained at 9 cm and 167,000 hills per hectare; this treatment also produced 156.5 tubers per plant and a thousand-tuber mass of 766.98 g. At 7 cm and the same density, yield reached 8,038.49 kg per hectare, with 153.0 tubers per plant and a thousand-tuber mass of 748.76 g. Root traits, tuber numbers in all three soil layers, and yield components were positively associated with yield. Overall, moderate deep sowing promoted root development and tuber formation, while 167,000 hills per hectare balanced individual growth and population productivity. The combinations of 7 or 9 cm sowing depth with 167,000 hills per hectare were recommended for high-yield Cyperus esculentus L. in sandy soils of Ejin Horo Banner. The identified 0–10 cm tuber concentration zone also provided a basis for optimizing the working depth of harvesting machinery under local sandy soil and irrigation conditions.