To quantitatively investigate the evolution of surface mesoscopic damagein nitrate ester plasticized polyether （NEPE） propellant during tension before and after aging， thermal accelerated aging tests were conducted with different aging days （0， 7 d， 40 d， 80 d）. An in-situ tensile machine combined with field emission scanning electron microscopy （FE-SEM） was employed for in-situ tensile testing， after which the captured images underwent digital processing. The fractal dimension was applied to quantitatively characterize and analyze the evolution of mesoscopic damage in the propellant at different aging stages. The differences between porosity method and fractal dimension method in characterizing mesoscopic damage before and after aging were studied. Results indicate that fractal dimension successfully captures the apparent damage evolution of NEPE propellant over different aging stages. During tension， for elongation below 20%， the fractal dimension rises relatively quickly with elongation. In the 20%-60% elongation range， the fractal dimension still increase with elongation， though at a reduced rate. Moreover， longer aging times were found to enhance the linear correlation between fractal dimension and elongation in this stage. Beyond 60% elongation， the fractal dimension shows irregular variation with elongation for all aging stages. Differences emerged between the porosity method and the fractal dimension method when characterizing the tensile process， especially after aging. While the porosity method mainly measuresthe area fraction of pores， the fractal dimension method characterizes the roughness and complexity of the surface morphology.