Viscoelastic damage properties of Nitrate Ester Plasticized Polyether (NEPE) solid propellant have been studied in cyclic loading tests. Both viscoelasticity and damage evolution of the material are considered. Based on the cyclic loading experiment results, a modified model containing a damageable spring is developed to characterize the viscoelasticity and damage evolution of NEPE propellant. With the material parameters obtained, a damage parameter D is defined, and the damage evolution curves for different loading conditions are predicted. It is shown that the critical damage parameter D-cr at the fracture points can be used to predict the fracture points at other loading conditions from the damage evolution curves with the material parameters obtained.