Ammonia (NH₃) is regarded as a promising medium of hydrogen storage, due to its large hydrogen storage density, decent performance on safety and moderate storage conditions. On the user side, NH₃ is generally required to decompose into hydrogen for utilization in fuel cells, and therefore it is vital for the NH₃-based hydrogen storage technology development to study NH₃ decomposition processes and improve the decomposition efficiency. Numerical simulation has become a powerful tool for analyzing the NH₃ decomposition processes since it can provide a revealing insight into the heat and mass transfer phenomena and substantial guidance on further improving the decomposition efficiency. This paper reviews the numerical simulations of NH₃ decomposition in various application scenarios, including NH₃ decomposition in microreactors, coupled combustion chemical reactors, solid oxide fuel cells, and membrane reactors. The models of NH₃ decomposition reactions in various scenarios and the heat and mass transport in the reactor are elaborated. The effects of reactor structure and operating conditions on the performance of NH₃ decomposition reactor are analyzed. It can be found that NH₃ decomposition in microchannel reactors is not limited by heat and mass transfer, and NH₃ conversion can be improved by using membrane reactors under the same conditions. Finally, research prospects and opportunities are proposed in terms of model development and reactor performance improvement for NH₃ decomposition.