In order to understand the influence of microstructure difference and thermal effect on the damage of PBX, a three-dimensional meso model is established using Voronoi method. The damage mechanism of PBX with different microstructure under thermal load is analyzed by considering the elasto-plastic properties of particles, the elasto-viscoplastic properties of binder and the interfacial cohesion constitutive relationship. The results show that the interface is not easy to be damaged when the temperature rises, but the binder with small shrinkage hinders the shrinkage of particles when the temperature decreases, resulting in the increase of the normal tensile stress between the interfaces, which is easy to cause interface damage. Increasing the content of binder is beneficial to reducing the damage of interface during cooling. When the binder content is similar, the more uniform the particle size is, the smaller the interfacial damage is. Under the action of low pressure, the damage changes from normal stress to tangential stress, and the damage decreases. However, when the pressure is too high, new damage occurs at the interface.