HMX with nanometer particle size and narrow particle distribution was successfully prepared by impinging method. The effects of different dispersants on particle size and particle size distribution were studied in some detail. It is concluded that dispersant 1 and dispersant 2 can improve considerably the particle distribution of HMX. In the presence of a suitable amount of dispersant 1,the obtained HMX has a effective average particle diameter of 70.1 nm and 68.9 nm,a particle distribution range of 0.9 nm and 1.4 nm respectively.