In order to investigate thermal decomposition properties and thermal stability of high energy density energy materials 2, 4, 6-triamino-3, 5-dinitropyridine-1-oxide(TANPyO), the adiabatic decomposition process of TANPyO was studied by accelerating rate calorimeter(ARC). Temperature rise rate, temperature and pressure versus time curves, pressure and temperature rise rate versus temperature curves were obtained, respectively. Results show that adiabatic decomposition process of TANPyO can be divided into two exothermic stages. The second stage is the main thermal decomposition process with a great change in temperature rise rate. The initial decomposition temperature of TANPyO is 252.7 ℃, which proves that TANPyO has good heat stability. Kinetic and thermodynamic parameters were calculated by temperature rise rate equation and Arrhenius equation are as follows: apparent activation energy 476.96 kJ·mol^-1, pre-exponential factor 6.920×10⁴² min^-1, reaction heat 930.84 J·g^-1, respectively.