In this paper, a numerical platform and plasma kinetics are developed to investigate the effects of non-equilibrium nanosecond plasma discharge, hydrogen, and oxygen mole percentages on ammonia combustion. It is shown that relatively high plasma energy densities or high mole percentages of H2 or O2 are needed to significantly enhance the flame speed of ammonia. O2 mole percentage has the least impact on ammonia reactivity among these three techniques. Increasing the contribution of plasma in assisting the flame results in less NOX emissions. The flame thickness of the ammonia flame varies non-monotonically by changing the arc energy and hydrogen mole percentage in the fuel, which is due to the radical pool in the flame preheating zone. Additionally, ammonia flame speed varies non-monotonically with O2 mole percentage in the air at high pulse energy densities.