To explore the thermal stability of 2, 6-diamino-3, 5-dinitropyridine-1-oxide(ANPyO), the adiabatic decomposition process of ANPyO was studied by accelerating rate calorimeter. The decomposition temperature, pressure and temperature rise rate versus time curves, and pressure and temperature rise rate versus temperature curves were obtained. Results show that adiabatic thermal decomposition process of ANPyO can be divided into two exothermic reaction stages. The first stage is the main decomposition one, in that the temperature rise rate has an obvious change. The apparent activation energy, pre-exponential factor and heat of reaction obtained by calculation are 293.61 kJ·mol^-1, 1.515×10²³ min^-1 and 940.92 J·g^-1, respectively. The initial decomposition temperature of ANPyO is higher than 290.8 ℃, showing a better thermal stability.