High sensitivity limits the broad application of CL-20 despite that it is considered as the most powerful explosive. Numerous efforts and technologies of fabricating CL-20 with small particle size have been implemented for solving this problem. In this study, CL-20 with sub-micron particle size was prepared by superfine comminution technique. The results of impact and friction sensitivities tests showed that the mechanical sensitivities of CL-20 were improved after ultra-fine treatment. DSC results showed that the decomposition of CL-20 advanced with the particle sizes decreased. The sub-micron sized CL-20 showed lower activation energy (E-alpha) compared to that of raw CL-20, suggesting that particle size reduction is in favour of decreasing the threshold of decomposition. The reaction models of CL-20 with different particle sizes could all be categorized as n-th order reactions with autocatalysis. The function of reaction mechanism could be expressed asf(alpha)=(1-alpha)(n)(1+k(cat)center dot alpha). On aspect of heat sensitivity, the results of deflagration point tests showed that although particle size had little influence on the deflagration point with 5 s delay time (T-b) of CL-20, apparent activation energy of explosion (E-b) decreased apparently with the particle sizes decreased, which could impact the thermal sensitivity significantly.