Behaviors of ignition and flame holding of a fuel jet by H-2/N-2 plasma torches in a supersonic air flow were numerically investigated by solving the two-dimensional Navier-Stokes equations with full chemistry of the H-2/N-2/O-2 reaction system. Three volumetric fractions of H-2 (0, 5, 30%) in a mixed feedstock gas were compared to determine the effect of the addition of H-2 to the feedstock. The H-2 included in the mixed feedstock quickly reacted with the main air flow after injection and the combustion gas covered the plasma jet (PJ) downstream. The effects of the combustion of H-2 molecules included in the feedstock strongly appeared in only the H-2 30%/N-2 70% PJ. The high-temperature region around the H-2 30%/N-2 70% PJ was enlarged and maintained for a long distance by the combustion and many radicals were included as secondary products in the jet. Moreover, the flame region around the H-2 30%/N-2 70% PJ developed more quickly and more widely than that of the H-2 5%/N-2 95% PJ. These effects of the combustion of H-2 molecules included in the feedstock are thought to be reasons for the superiority of the H-2 30%/N-2 70% PJ to other PJs such as a N-2 PJ or an O-2 PJ examined in past experiments.