AbstractTo better understand the mechanical properties and influence mechanism of hydroxyl‐terminated polybutadiene (HTPB) propellant under various confining pressures, the uniaxial tension tests with low to medium strain rate and various confining pressures were carried out. The coupling effects of strain rate and confining pressure on mechanical properties were presented. Meanwhile, the confining pressure influence mechanism was analyzed and revealed using the meso numerical simulation method and scanning electron microscopy images of fracture surfaces. The meso damage evolution processes under various confining pressures were presented. The results show that strain rate and confining pressure affect mechanical responses of HTPB propellant significantly. As confining pressure increases, the maximum tension strength and fracture strength increase. The maximum tension strain and failure strain vary slightly with confining pressure under low strain rate, while they increase significantly with confining pressure at medium strain rate. The fracture energy density increases with the increase of strain rate and confining pressure. Meanwhile, the value of saturation pressure depends on strain rate. The confining pressure influence mechanism is to suppress dewetting damage initiation and evolution. Besides, the failure mode of HTPB propellant under different confining pressures is still particles dewetting.