Farmland soil is the main source of anthropological nitrous oxide (N2O) emission, and elevated atmospheric carbon dioxide (eCO2) can enhance crop growth and plant biomass carbon attribution into the soil, consequently promoting soil denitrification process to increase field N2O emission. Crop straw incorporation into soil, an increasing common practice of crop management, might regulate the effect of eCO2 on N2O emission through changing soil organic carbon availability. In order to learn the regulation effect and its underlying mechanism, therefor we conducted a comprehensive study with both field and pot experiments under open-top chamber condition. Our study showed that there was a similar enhancement of eCO2 effect on wheat aboveground biomass by 15.1% without straw and 17.3% with straw incorporation. However, eCO2 and straw incorporation had a significant interaction effect on N2O emission, that is, eCO2 increased N2O emission by 17.1% with non-straw incorporation, but that was 28.1% with straw incorporation. Meanwhile, eCO2 increased the ratio of importance functional genes (nirK+nirS)/nosZ in the denitrification process in straw returning, which was about 13.8% higher than that in straw non-returning. Our study demonstrates that the effect of eCO2 on soil N2O emissions may be underestimated by existing studies, implicating that it is urgent to innovate crop management practice for high yield and low N2O emission in future eCO2.