Abstract: To solve the problem of excessive downstream deformation of propellant grain with a radial annular groove structure inside a solid rocket motors, a two-way fluid-structure interaction analysis method was adopted. The effects of propellant elastic modulus, annular groove geometry, and groove layout on the downstream outlet deformation of the annular groove were investigated. Furthermore, targeted optimization schemes for the downstream profile of the annular groove were proposed. The results indicate that at the beginning of the motor operation, a localized high-pressure gradient forms at the downstream exit of the annular groove. Such a pressure gradient triggers a shrinkage deformation of the propellant grain, which in turn exacerbates the pressure gradient within the solid computational domain. Sensitivity analysis demonstrates that the deformation at the downstream exit of the annular groove is correlated with the annular groove geometry and the propellant modulus, whereas the influence of the groove layout is relatively weak. To mitigate the adverse effects of fluid-structure interaction, a chamfer structure is machined on the cross-section at the downstream exit of the annular groove to expand the flow area. After this structure optimization, the pressure drop at the monitoring point at the downstream exit of the annular groove in the fluid domain is reduced by 80%. Concurrently, the axial displacement at the monitoring point in the downstream exit in the solid domain is decreased by 84.55%, and the radial displacement is decreased by 90.66%.