Energetic materials are widely used as propellants, explosives and pyrotechnics. To allow the safe development and effective use of energetic devices, it is important to understand reaction mechanisms and thermal properties of energetic materials. Thermal analysis is a strong tool to investigate reaction of energetic materials. In this paper, reaction scheme and thermal behavior of ammonium dinitramide, which is one of the most promising next generation oxidizer of rocket propellants, are analyzed experimentally and theoretically. DSC, TG-EGA, DSC-Raman studies have been carried out to measure the heat of reaction and decomposition products, and quantum chemistry calculation have revealed possible reaction pathways.