To investigate the damage evolution process of low-frequency fatigue-loaded NEPE (nitrate ester plasticized polyether) solid propellant and get the influence law of fatigue loading history on tensile mechanical properties of NEPE solid propellant, the NEPE solid propellant low-frequency fatigue tests and uniaxial tensile tests with constant strain rate were conducted by the electronic universal testing machine. Based on the microscopic morphology and testing curves of test piece after fatigue loading, the influential mechanism of microscopic and mesoscopic damage on the NEPE solid propellant macroscopic mechanical behavior was further analyzed. Results indicate that the NEPE solid propellant matrix microcracks and voids at the matrix/particle interface are induced by low-frequency fatigue loads, leading to nonnegligible stress-softening behavior and residual strain. During and after fatigue loading, the attenuations of macroscopic mechanical properties of NEPE solid propellant are all exponentially related to the maximum loading strain. Part of microscopic damage by low-frequency fatigue load can recover, while the remaining fatigue damage may enhance the molecular chain orientation ability, and thus lead to the fatigue-strengthening phenomenon in materials.