Uniaxial tensile testing and short-term tensile creep testing within several hours for a long-term thermally aged polymer bonded explosive (PBX) within years were conducted to evaluate the aging effects in terms of mechanical properties. Dumbbell specimens were thermally aged at 45, 55, 65 ℃ and 75 ℃ respectively for 36 months. The quasi-static tensile strength testing was conducted at 45 ℃. The tensile creep testing for 6 month and 36 month thermally stored specimens were carried out at controlled temperature of 45 ℃. The results show that the tensile mechanical properties, such as tensile strength and elastic modulus essentially keep unchanged compared to the pristine specimens, but the creep time to rupture (TTR) of the thermally treated specimen becomes much longer than the pristine specimens except for 75 ℃. Combining scanning electronic microscope(SEM) observation and contacted angle analysis, we proposed that the mechanical failure for the targeted PBX was controlled by the thermal rheological mechanism of the ingredients when aged temperature is below 55 ℃, but when temperature is above 55 ℃; the failure was controlled by thermal stresses mismatch around the interface between the binder and the explosive crystals in the formulation. The long-term thermally storage below 75 ℃ for this PBX can improve the creep performance in terms of TTR.