New experimental results of the characteristics of fuel-NOx formation at high CO2 concentrations are obtained in a jet-stirred reactor. NH3 is selected as the source of N. The effects of the CO2 concentration (0-97.4%), reaction temperature (873-1323 K), equivalence ratio (0.56-1.61), initial NH3 concentration (10-1000 ppm) and residence time (0.01-10 s) on the production and destruction of fuel-NOx are experimentally and numerically investigated in both N-2 and CO2 atmospheres. Under fuel-lean conditions, the NO emissions decrease with increasing residence time, equivalence ratio, or CO2 concentration. Under stoichiometric conditions, the NO productions from the N-2 and CO2 atmospheres are nearly the same, irrespective of the temperature. Under fuel-rich conditions, the NO-reburning chemistry can reduce the majority of the NO. Under fuel-rich conditions and at temperatures above 1200 K, the NO production is lower in the N-2 atmosphere because the NO-reburning is stronger than in the CO2 atmosphere. Moreover, the critical temperature for the peak N2O formation is obtained. Although fuel oxidation is slightly delayed at high CO2 concentrations, N2O formation is essentially insensitive to the CO2 concentration. Furthermore, the numerical results are consistent with the vast majority of experiments, and important reactions are identified for future development of fuel-NOx formation at high CO2 concentrations.