The ignition mechanism of the explosive particles under impact has been a hot topic, but the research progress is slow. With the rapid development of computer science, the three-dimensional discrete element technique (DM3) is regarded as an efficient and intuitive method to study the explosive ignition under impact. As is well known, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is one of the most effective explosive particles in performance, which has high density and energy and thus possesses a significant application. In this paper, the deformation and ignition of HMX particles under impact of drop hammer are investigated based on the three-dimensional discrete element technique. Specifically, the computational process for shock loading as well as chemical reaction is employed in DM3 model through using the state equation of Hugoniot, the reactive model of Arrhenius, the state equation of JWL. The results show that the size, degree of accumulation, defect and the force of drop hammer can definitely influence the ignition and propagation of HMX particles. Under the same shock loading, the particles on a small scale would produce less power. On the same scale of particle, the less the number of particles, the shorter the deformation time is, so the temperature increases more easily. As for the different shapes of single particles, the deformation and ignition first appear from the ‘top’ for the spire particles, and then the deformation and ignition of flat particles happens from ‘shear’. Specifically, there are two results of the internal defect HMX particles under impact: the particles with bigger size (discrete elements 256 × 34 = 8704) have a temperature advantage near the ‘hole’, while the temperature advantage of the particles with the smaller size (discrete elements 93 × 35 = 3814) appears on the ‘top’.