AbstractWith the purpose of investigating the influences of aging time and confining pressure on the mechanical properties of a composite modified double‐based (CMDB) propellant, uniaxial tension tests of the propellant with various accelerated aging times were conducted under various confining pressure conditions (relative atmospheric pressure 0, 0.5±0.05, 2±0.05 and 6±0.05 MPa). The stress‐strain behaviors at various experimental conditions were analyzed. The results show that stress‐strain curves can be divided into three stages, the initial tensile stage, the elastic stage, and the damage growth stage. Additionally, the key mechanical parameters (e. g., the maximum tensile strength) show a strong dependence on aging time and confining pressure. The ultimate strain decreases with increasing aging time, while the tensile strength first decreases and later increases with aging time. It was observed that the maximum tensile strength and elastic modulus of the CMDB propellant decrease with confining pressure. Furthermore, the damage evolution curves can be divided into two stages. The later nonlinearity of the stress‐strain curves is mainly induced by the initiation and propagation of macro‐cracks. It is believed that these findings will help to accurately analyze the structural integrity of CMDB propellant grains during ignition pressurization loading after a long storage time.