Abstract: Pressurized curing, owing to its remarkable capability in reducing curing residual stresses, has emerged as a frontier technology in the manufacturing of solid propellant grains. The fluid-to-solid transition occurring during the pressurized curing of solid propellants poses a significant challenge for the unified characterization of the mechanical behavior throughout this process. Current research on constitutive modeling and experimental testing for pressurized curing process remains insufficient, which in turn constrains the advancement of technologies aimed at controlling grain curing residual stresses. To address this gap, a nonlinear viscoelastic constitutive model for the pressurized curing process of solid propellants was developed. This model considers the coupled effects of temperature and pressure, employs the degree of cure as an internal state variable, and incorporates cure reaction kinetics. Using nitrate ester plasticized polyether (NEPE) propellant as the subject material, experiments were conducted to measure the evolution of its viscosity, stress relaxation behavior, and nonlinear mechanical response. Model parameters were determined based on the experimental data, and the model's accuracy was subsequently validated. Building on this foundation, the pressurized curing process of an NEPE propellant in a cylindrical grain configuration was numerically investigated. The evolution regularities of curing residual stresses and strains within the grain during the process was revealed. Furthermore, the influences of various factors, including gravity, curing pressure, and the selection of different constitutive models, on the predictions of residual stresses were analyzed. The results demonstrate that the constructed constitutive model can accurately describe the evolution of the mechanical behavior of NEPE propellant throughout the pressurized curing process. Importantly, all model parameters can be obtained through conventional laboratory tests. The findings of this study establish a theoretical foundation for developing advanced techniques to control curing residual stresses in propellant grains. Additionally, the methodology and insights presented may serve as a valuable reference for research on the curing processes of other thermosetting resin-based composites.