Abstract: In order to investigate the effects of biochar on soil CO₂ emissions, water use efficiency, and yield under regulated deficit irrigation, a field plot experiment was conducted using the summer maize-winter wheat rotation system as the research object during 2021—2022 and 2022—2023. In the summer maize experiment, three irrigation modes were set (WI: conventional irrigation, WJ: deficit irrigation from jointing to anthesis, WA: deficit irrigation from silking to grain filling) and three levels of biochar application (B0: no biochar, B15: biochar applied at 15 t/hm², B30: biochar applied at 30 t/ hm²). In the winter wheat experiment, three irrigation modes were set (WI: conventional irrigation, WJ: deficit irrigation from jointing to heading stage, WA: deficit irrigation from flowering to grain-filling stage) and three levels of biochar application (B0: no biochar, B15: 15 t/hm² biochar, B30: 30 t/hm² biochar). A two-factor randomized block design was used, with a total of 9 treatments.The results indicate that: 1) Under irrigation conditions, the application of biochar (B15, B30) promoted soil CO₂ emissions, with total emissions increasing by 2.54% to 15.98% compared with the control; whereas deficit irrigation (WJ, WA) inhibited CO₂ emissions, with total emissions under biochar treatments reduced by 3.31% to 12.19% compared to conventional irrigation. 2) Soil CO₂ emission flux was significantly positively correlated with soil moisture, temperature, and pH (correlation coefficients of 0.655, 0.991, and 0.45, respectively), and also positively correlated with organic carbon content. 3) From 2021 to 2023, the WAB30 treatment performed excellently in terms of yield and water use efficiency, with yields reaching 16,598.47 kg/hm² and water use efficiency of 20.81 kg/(hm²·mm) in 2022–2023, while maintaining low CO₂ emission intensity (1.10 kg/kg). In summary, the WAB30 treatment (deficit irrigation during the booting stage combined with 30 t/hm² of biochar) can achieve lower CO₂ emission intensity while maintaining high yield and water use efficiency.