The thermal stability of a new plastic bonded explosive PBX-HKF composed of main explosives (HMX and potassium picrate), plasticizer and binder, has been studied by an accelerating rate calorimeter. The curves of thermal decomposition temperature and pressure versus time，self-heating rate and pressure versus temperature were obtained. According to adiabatic theory, the activation energy E_a=337.32 kJ·mol^-1 and pre-exponential factor 9.32E34 s^－1 are obtained. The decomposition history and safety of PBX-HKF were analysed. It is indicated that the new plastic bonded explosive possesses very good.