To investigate the effect of non-equilibrium plasma on the combustion of ammonia/air at ambient conditions, the CHEMKIN software was used to simulate the ignition delay time of ammonia/air under experimental conditions. The ZDPlaskin program was used to study the discharge of ammonia/air at ambient conditions. The resulting O, H, and OH radicals were used as the CHEMKIN initial conditions to study the effect on the ignition delay time of ammonia/air. The sensitivity of the temperature and active radicals at the ignition time were analyzed. The results from ZDPlaskin show that the number density of radical particles produced by discharge of mixtures with different equivalence ratios was similar. The simulation results of CHEMKIN indicate that without the addition of free radicals, the ignition delay time is less affected by the change of equivalence ratio when the equivalence ratio is 0.8 ~ 1.2. After the addition of free radicals, the ignition delay time decreases with the decrease of equivalence ratio. O. H and OH radicals can significantly reduce the ignition delay time of ammonia/air, and the degree of reduction decreases with the increase of initial temperature. At the same initial temperature, the reaction equation is the same as the reaction equation with the highest temperature sensitivity, as the temperature increases, the reaction equation with the highest sensitivity will change and the sensitivity will significantly decrease. At different initial temperatures, multiple reactions appear repeatedly in the reactions with the highest temperature and radical sensitivity, which is an important basis for simplifying the mechanism.