Abstract: A computational representative volume element (RVE) framework considering interface, as well as particle morphology, was adopted to provide a better understanding and prediction of the existing links between the behaviors of contents, interface and the macroscopic mechanical responses of composite solid propellants. A cohesive zone model (CZM) was taken into account to study the significance of interface stiffness, strength and critical displacement, along with the relative contribution of particle morphology and interface, on the macroscopic mechanical properties of the propellant. Results indicate that the initial modulus of propellant increases from 0.67 MPa to 3.67 MPa as the interface stiffness varies between 0.004 MPa/mm and 400 MPa/mm, while the tensile strength of propellant increases from 0.15 MPa to 0.76 MPa when the interface strength changes from 0.05 MPa to 30 MPa, which implies that an increase in the interface stiffness has a limited improvement over the initial modulus of the propellant. In comparison, the interface strength improves its tensile strength remarkably. However, higher interfacial strength may lead to “damage localization” in the microstructure, thus reducing the elongation of propellant. The different behaviors observed on macroscopic view are rather due to interface than to the morphology of particles; all of the results exhibit that the interface is one of the major determining factors affecting the tensile properties of the propellant. Finally, based on the previous analyses, the creep behaviors of another propellant were predicted under various stress levels. It is found that the logarithm of creep rupture time is linear with constant stress.