This study extensively investigated the thermal decomposition process of NH4V3O8, examining how varying temperatures affect the physicochemical properties of the products, as well as exploring the mechanism and kinetics of the process. Through XRD and SEM analysis, the study identified the phase compositions, crystal structures, and micromorphology of the thermal decomposition products. It also systematically investigated the effects of temperature on particle size and specific surface area, identified the lowest thermal decomposition temperature, and proposed the reaction equations. Additionally, by employing FT-IR analysis and DFT calculation, the study revealed the molecular-level thermal decomposition mechanism of NH4V3O8. Finally, the study calculated the kinetic parameters of NH4V3O8 thermal decomposition using the Kissinger and Kissinger-Crane methods and established the rate equation. These findings not only provide practical guidance but also serve as theoretical references for the thermal decomposition of other metal ammonium salts.