Though ammonia (NH3) is one of the most highly produced inorganic chemicals in the world, its pollution disadvantage on air and water have drawn much attention. In this article, the NH3 removal is investigated through pulse discharge method. A zero dimensional molecular reaction model is established and solved. The vapour assisting effect on the NH3 gas removal is discussed due to the extremely soluble character of NH3. Simulation indicates that the vapour additive has affected the H2 and N2 generating process. For vapour with several thousand’th ratio mixed, the electron collision on H2O has been ignored. The results show that lower concentration vapour improves the removal efficiency in a very small extent, but higher vapour deteriorates it, with the optimal mixing concentration ratio between H2O and NH3 as 0.75:1000. For vapour with several tenth ratio mixed, the electron collision process on H2O molecules is considered. More H2O additive has significantly improved the NH3 removal efficiency by accelerating the H2 and N2 generation process. At the vapour ratio of 750‰, the removal efficiency is 64.28%, which is remarkably higher than that of 37.81% without vapour added. H2O additive has saving of 70% energy consumption. The initial NH3 concentration is another factor to influence the removal efficiency. The higher the initial NH3 input, the less the H2O is decomposed into OH and H by electron impact, and the removal efficiency is decreased consequently.