Three kinds of HMX samples with different morphologys and particle sizes were prepared by screening,ball milling or solvent/nonsolvent methods,respectively,and characterized by laser granularity measurement and scanning electron microscope (SEM). The mechanical sensitivity and thermal decomposition of the samples were studied by impact sensitivity test,friction sensitivity test and DSC analysis. Results show that there are no obvious trends of the mechanical sensitivities depending on its d₅₀ for screening samples. However,for ball milling samples,the impact sensitivity reduces,and the friction sensitivity increases as its d₅₀ decreases. For solvent/nonsolvent samples,both the impact sensitivity and friction sensitivity decrease as its d₅₀ decreases. Moreover,the average value of activation energy of thermal decomposition for ball milling samples is 262.184 kJ·mol^-1,which is much higher than that (238.902 kJ·mol^-1 and 242.343 kJ·mol^-1) for the samples prepared by solvent/nonsolvent and screening methods.