To study the formation mechanism of residual stress/strain of the nitrate ester plasticized polyether （NEPE） propellant grain during the curing and cooling stages， the temperature field， curing degree field and stress/strain field of the propellant were numerically analyzed via ABAQUS finite element software. The results show that there are temperature gradient and curing rate gradient in the NEPE propellant grain during the curing process at 50 ℃. The temperature and the curing rate are notably higher at the center of the grain， and they eventually reach a consensus at the end of curing. The temperature difference in the propellant does not affect the final residual stress/strain. The total residual stress/strain during curing and cooling obey the principle of stress/strain superposition， and they are mainly composed of the curing shrinkage stress/strain and thermal stress/strain during cooling. For the total residual stress， the proportions of the two stages are approximately 20% and 80%， respectively， and for the total residual strain， the proportions are about 30% and 70%， respectively. Compared with the traditional method， the residual stress/strain calculated in this study have the same distribution characteristics， but the values are smaller.