It is difficult to directly observe the microscopic behavior of particles and the evolution of force chains in the process of polymer bonded explosive (PBX) compacting. To solve this problem, a discrete element method model of PBX compaction was established, which considered the non-spherical morphology and fragmentation behavior. Through the density, porosity, average coordination number and force chain network evolution in the process of compaction, the influence of compaction pressure and speed on the forming quality of grain was analyzed. The results show that the compaction process of PBX can be divided into three stages: particle breakage and rearrangement, rapid densification and stable compaction, and the force chain evolves from discrete to continuous bearing network; When the pressure increases from 150 to 300 MPa, the average density increases from 1.570 to 1.682 g/cm3, the porosity decreases obviously, and the average coordination number increases; The compaction speed mainly affects the compaction time, but has little effect on the final molding quality. Under the fixed compaction pressure, when the compaction speed increases from 0.5 to 3 mm/s, the density range is 0.007 g/cm3, and the porosity and coordination number do not change significantly. The research results can provide a theoretical basis for the optimization of process parameters and the quality control of PBX grain in the process of compression molding.