HTPB propellant is the high filled particulate elastomeric matrix composite. Debonding of particle/matrix interfaces can significantly affect the macroscopic behavior of composite propellant. How to model the propellant material and describe damage processes to discover damage mechanism has been a long-standing question. This paper used the bilinear cohesive law with different parameter values for particle/matrix interfaces to study interface debonding. By analyzing the damage evolution in two model particulate composite systems with finite element method, the scheme was shown to capture effects associated with the interface strength and the interactions between particles.