Abstract: Two groups of Mn metal fuels with different particle-size distributions were prepared with median diameters of 18.73 and 5.24 μm. The particle-size distribution was measured by a laser particle-size analyzer, the surface morphology was analyzed via scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) determined the contained elements. For the NaClO₃, the NaClO₃ and Co₃O₄ as well as NaClO₃, Co₃O₄, and Mn mixtures were subjected to TGA-DSC combined thermogravimetric analysis. The effects of the Mn metal fuel particle size on the catalytic effect and pyrolysis stability of NaClO₃ were investigated by comparing the pyrolysis onset/final temperature and other characteristics. The results show that although Co₃O₄ has a significant catalytic effect on the pyrolysis of NaClO₃, e.g., the onset pyrolysis temperature decreases from 512.3 to 333.0℃, it can lead to instability in NaClO₃ pyrolysis, namely the pyrolysis steps from 1 to 3. The Mn metal fuel has a clear catalysis effect on the intermediate products of NaClO₃ pyrolysis. With the decrease in particle size, the catalytic effect gradually increases and the pyrolysis final temperature T_f decreases from 419.8 to 351.9℃. Meanwhile, the pyrolysis step of NaClO₃ decreases and the temperature range of pyrolysis decreases from 180.6 to 19.4℃, indicating that the pyrolysis process becomes more stable.