Ammonia, made up of 17.8% hydrogen, has attracted a lot of attention in combustion community due to its zero carbon emission as a fuel in gas turbines. However, ammonia combustion still faces some challenges including the weak combustion and sharp NOx emissions which discourage its application. It was demonstrated that the combustion intensity of ammonia/air flame can be enhanced through adding active fuels like methane and hydrogen, while the NOx emission issue will emerge in the meantime. This study investigates regulation effect of methane and hydrogen on the emission characteristics of ammonia/air flame in a gas turbine combustor. The instantaneous OH profile and global emissions at the combustion chamber outlet are measured with Planar Laser Induced Fluorescence (PLIF) technique and the Fourier Transform Infrared (FTIR), respectively. The flames are also simulated by large eddy simulation to further reveal physical and chemical processes of the emissions formation. Results show that for NH3/air flames, the emissions behavior of the gas turbine combustor is similar to the calculated one-dimensional flames. Moreover, the NOx emissions and the unburned NH3 can be simultaneously controlled to a proper value at the equivalence ratio (φ) of approximate 1.1. The variation of NO and NO2 with φ for NH3/H2/air flames and NH3/CH4/air flames at blending ratio (Zf) of 0.1 are similar to the NH3/air flames, with the peak moving towards rich condition. This indicates that the NH3/air flame can be regulated through adding a small amount of active fuels without increasing the NOx emission level. However, when Zf = 0.3, we observe a clear large NOx emission and CO for NH3/CH4/air flames, indicating H2 is a better choice on the emission control. The LES results show that NO and OH radicals exhibit a general positive correlation. And the temperature plays a secondary role in promoting NOx formation comparing with CH4/air flame. •The regulation effects of methane and hydrogen on NOx emission of ammonia/air flames in a swirl combustor are investigated.•The emission characteristics are verified similar between 1D simulation and the experimental results.•The flame structure detected by OH-PLIF is used to reveal NO emission qualitatively.•The relation of NO and OH is revealed by LES for the NH3/CH4/air flame.