In order to investigate the micro-damage of hydroxyl-terminated polybutadiene (HTPB) propellant under tensile loading, interface models of ammonium perchlorate (AP)/HTPB and AP/HTPB/AP were established. Based on classical molecular dynamics, the deformation and failure behavior of the interface models under uniaxial tension were calculated. The influence of temperature on the mechanical properties of the interface models was analyzed, and the stress-strain curves and energy change curves of the interface models were obtained. The calculation results showed that micro cavities would appear inside the HTPB layer under axial loading. As the strain increased, the micro cavities merged, and the final failure location of the interface model was near the interface. The nominal stress-strain curve of the interface model could be divided into four stages: approximately linear elastic, yield, stress strengthening, and interface failure. As the temperature increased, the failure stress of the interface model decreased, and the elongation rate showed no significant change.