【Objective】 Intercropping maize with leguminous green manure can achieve fertilizer conservation and efficiency improvement. Biochar application is an effective measure to mitigate gaseous nitrogen loss form farmland. However, the impacts of nitrogen reduction under intercropping green manure combined with the biochar application on gaseous nitrogen loss and the system’s nitrogen footprint remain unclear. This study aimed to evaluate this comprehensive practice to provide a technical approach for the green maize production in oasis irrigation areas of Northwest China. 【Method】 A two-factor field experiment was set up in 2021 at Wuwei Oasis Agricultural Experimental Station in Gansu Province. The experiment employed a two-factorial design. The main factor was nitrogen application system, including conventional nitrogen application (N100), 30% nitrogen reduction (N70), and 30% nitrogen reduction combined with sesbania biochar (N70S). The second factors were cropping patterns, including maize monoculture (MM) and maize intercropping with common vetch (IMC). Six treatments were formed: N100-MM, N100-IMC, N70-MM, N70-IMC, N70S-MM, and N70S-IMC. From 2024 to 2025, maize yield, nitrogen absorption and soil physicochemical properties were measured, nitrous oxide emission and ammonia volatilization were monitored, and the nitrogen footprint of the system was quantified by life cycle assessment method. 【Result】 Compared with N100, N70 decreased maize grain yield, aboveground biomass and nitrogen absorption by 7.9%, 6.1% and 4.7%, respectively. In contrast, N70S increased grain yield and biomass by 8.6% and 2.7%, respectively. IMC increased the yield by 3.8% compared with MM. Notably, N70S-IMC increased grain yield, aboveground biomass and nitrogen absorption by 12.6%, 4.3% and 4.0%, respectively, compared with N100-MM. The N70 reduced cumulative N₂O emissions and NH₃ volatilization by 16.0% to 25.2% and 9.9% to 24.7%, respectively, relative to N100. The N70S further reduced these emissions by 24.8% to 27.7% and 17.6% to 43.9%, respectively. Compared with N100-MM, N70-IMC and N70S-IMC reduced cumulative N₂O emissions by 12.1% to 20.1% and 20.1% to 35.8% and NH₃ volatilization by 15.3% to 24.3% and 11.2% to 20.1%, respectively. Soil analysis showed that, compared with N100-MM, N70-IMC decreased soil ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), and microbial nitrogen (MBN) by 17.6%, 15.6%, and 9.6%, respectively. While N70S-IMC decreased NH₄⁺-N and soluble organic nitrogen (DON) by 15.6% and 7.3%, respectively, but increased total nitrogen (TN) and MBN by 3.9% and 25.0%, respectively. Random forest analysis indicated that soil NO₃^--N, NH₄⁺-N, MBN and DON were the key factors driving N₂O emissions, while NH₃ volatilization was mainly driven by NO₃^--N, NH₄⁺-N and TN. Life cycle assessment indicated that the nitrogen footprint under N70-IMC and N70S-IMC was decreased by 28.9% and 39.7%, respectively, compared with the N100-MM. Furthermore, the nitrogen footprint of the N70S-IMC treatment was 10.4% lower than that under N70-MM. 【Conclusion】 The combination of maize-green manure intercropping, 30% nitrogen reduction, and sesbania biochar application increased grain yield and nitrogen absorption, improved key soil properties, and lowered N₂O emissions, NH₃ volatilization, and the system’s nitrogen footprint, which was an effective path for green and sustainable maize production in the Northwest Oasis Irrigation District.