Ammonia, a promising carbon-free fuel, offers significant potential for reducing carbon emissions. The decomposition of NH3 is crucial for improving NH3 combustion, yet its mechanisms remain unclear. This study uses ReaxFF simulations, density functional theory (DFT), and Chemkin calculations to explore NH3 decomposition and refine the Konnov mechanism. Our results show that the NH3 to N2 conversion is highly temperature-dependent. At high temperatures, the pathway is NH3→NH2→N2H4→N2H2→N2. As temperature decreases, the N2H pathway becomes more significant, shifting the reaction to NH3→NH4→NH2→N2H→N2 pathway. Additionally, temperature affects H dissociation: at lower temperatures, NH3 to NH2 follows NH3→NH4→NH2, while the NH4 pathway's influence diminishes with rising temperatures. The updated Konnov mechanism improves NH3 decomposition prediction accuracy by about 72.79% and enhances predictions of decomposition rates and intermediate formations (NH, NH2, NH4). This research advances the understanding of NH3 decomposition mechanisms and is vital for optimizing burners for efficient and stable NH3 combustion.