Abstract: Thermal decomposition of a famous high oxidizer ammonium dinitramide (ADN) under high temperatures (2000 and 3000 K) was studied by using the ab initio molecular dynamics method.Two different temperature-dependent initial decomposition mechanisms were observed in the unimolecular decomposition of ADN, which were the intramolecular hydrogen transfer and N-NO₂ cleavage in N (NO₂)^-.They were competitive at 2000 K, whereas the former one was predominant at 3000 K.As for the multimolecular decomposition of ADN, four different initial decomposition reactions that were also temperature-dependent were observed.Apart from the aforementioned mechanisms, another two new reactions were the intermolecular hydrogen transfer and direct N-H cleavage in NH₄⁺.At the temperature of 2000 K, the N-NO₂ cleavage competed with the rest three hydrogen-related decomposition reactions, while the direct N-H cleavage in NH₄⁺ was predominant at 3000 K.After the initial decomposition, it was found that the temperature increase could facilitate the decomposition of ADN, and would not change the key decomposition events.ADN decomposed into small molecules by hydrogen-promoted simple, fast and direct chemical bonds cleavage without forming any large intermediates that may impede the decomposition.The main decomposition products at 2000 and 3000 K were the same, which were NH₃, NO₂, NO, N₂O, N₂, H₂O, and HNO₂.