Structural function of stress release cover in solid motor was analyzed by using incremental viscoelastic impressible FEM. The results show that, although the stress release cover has no beneficial effects on decreasing strain strength on internal surface of middle solid propellant grain, it can reduce cladding/interface interfacial stress level which is beneficial for maintaining structural integrity of solid motor, and can minish the ballistic deformation of ends of solid propellant, which is beneficial for stabilizing interior trajectory performance of solid motor.