The thermal safeties of three kinds of firework (70/20/10-KClO₃/Al/S, 70/20/10 KNO₃/Al/S, and 67/20/13 KClO₄/Al/S mixture) were studied by accelerating rate calorimeter(ARC). The curves of thermal decomposition temperature and pressure versus time, and the reaction rate versus temperature were obtained, moreover, the thermal decomposition processes were discussed. The apparent activation energy and pre-exponential factor of this reaction were also calculated. The results show that the thermal safety of potassium chlorate mixture is the lowest among the three kinds of firework.