Ecosystem CO2 and N2O exchanges between soils and the atmosphere play an important role in climate warming and global carbon and nitrogen cycling; however, it is still not clear whether the fluxes of these two greenhouse gases are correlated at the ecosystem scale. We collected 143 pairs of ecosystem CO2 and N2O exchanges between soils and the atmosphere measured simultaneously in eight ecosystems around the world and developed relationships between soil CO2 and N2O fluxes. Significant linear regressions of soil CO2 and N2O fluxes were found for all eight ecosystems; the highest slope occurred in rice paddies and the lowest in temperate grasslands. We also found the dominant role of growing season on the relationship of annual CO2 and N2O fluxes. No significant relationship between soil CO2 and N2O fluxes was found across all eight ecosystem types. The estimated annual global N2O emission based on our findings is 13.31 Tg N yr−1 with a range of 8.19–18.43 Tg N yr−1 for 1980–2000, of which cropland contributes nearly 30%. Our findings demonstrated that stoichiometric relationships may work on ecological functions at the ecosystem level. The relationship of soil N2O and CO2 fluxes developed here could be helpful in biogeochemical modeling and large-scale estimations of soil CO2 and N2O fluxes.