Abstract: In this study, to address issues such as the low soil carbon and nitrogen reserves and continuous decline in soil quality in the Hexi Oasis irrigation area, we assessed the effects of tillage practices and the incorporation of straw on soil aggregates and carbon–nitrogen reserves in cornfields. To this end, we established the following four treatments: traditional tillage + no straw return (CT), traditional tillage + straw return (TS), no-till + no straw return (NT), and no-till + straw return (NTS). The results indicated that tillage practices, straw return, and their interaction had significant effects on soil organic carbon (SOC) and total nitrogen (TN) reserves in the 0–30 cm soil layer (P < 0.05). Compared with conventional tillage (CT), no-till with straw incorporation significantly increased the contents of SOC and TN (P < 0.05), with the NTS treatment contributing to the highest reserves at 14.65–15.00 Mg(C)∙hm⁻² and 1.44-1.46 Mg(N)∙hm⁻², respectively. Under the same straw treatment, compared with conventional tillage, the no-till treatment contributed to significant increases in the contents of SOC and TN of 5.3%–7.6% and 9.2%–11.8%, respectively (P < 0.05). Under the same tillage treatment, the incorporation of straw resulted in significant increases of 3.6%–3.7% and 4.6%–5.9% in SOC and TN, respectively (P < 0.05) compared with non-incorporation. Macroaggregates of ≥0.25 mm in size were found to contribute most to the SOC and TN contents in soil, with their contribution declining with increasing soil depth. Compared with that of CT, their contribution under the NTS treatment was significantly higher by 18.6%–28.5% and 20.6%–27.9%, respectively (P < 0.05). No-till straw incorporation was found to promote increases in SOC and TN primarily by enhancing the contents of 0.25–1 mm macroaggregates, thereby increasing the mean weight diameter and geometric mean diameter of the soil aggregates, reducing the fractal dimension, and improving aggregate stability. The results of structural equation modeling indicated that the stability of ≥0.25 mm large aggregates was significantly positively correlated with the storage of carbon and nitrogen, increases in which are dependent on the enhancement of carbon and nitrogen content within soil aggregates. Consequently, both no-till farming and straw incorporation contribute favorably to enhancing soil aggregate stability and promote increases in carbon and nitrogen storage in farmland soils. Among the different combination treatments assessed, the NTS treatment was established to have the best soil improvement effects in the plow layer, and we found that increases in soil carbon and nitrogen storage are dependent on enhancement of the carbon and nitrogen contents within soil aggregates.