Abstract: Based on the micromechanical damage characteristics of composite solid propellants, a cohesive interface element was placed between particles and binder. The bilinear model was used to describe interfacial damage evolution, and its key parameters were determined, including the intial linear modulus, maxmial cohesive strength, and maximal displacement. Combined with packing models of composite solid propellant, the micromechanical interfacial debonding was analyzed by finite element method. The results show that cohesive interface element can effectively predict the progress of debonding of particles from binder. The nonlinear mechanical properties of propellant under tensile is closely related with interfacial debonding. The numerical results are in agreement with the experimental observations.