Since long term, the reliability problem of a solid rocket motor has been highly considered, and especially probability design has already become an absolutely necessary tache during designing and manufacturing solid rocket motors. A solid rocket motor is a complicated system which can be used only once and can not be repaired. Because of the effect of the random factors such as high temperature, high pressure, high heat flow and so on, the motor is prone to fail and even results in contretemps when it can not work as preset sequence or has inherent defect in its structure. So it is very necessary to do research in the structural integrity and the structural reliability of solid rocket motors on the basis of theoretics and engineering practice.As a significant ingredient of a solid rocket motor, the structural integrity and the structural reliability of the solid rocket motor grain can directly influence the reliability of the whole solid rocket motor.According to one solid rocket motor ,this paper has accomplished the study on the structural integrity and the structural reliability of the solid rocket motor grain. Firstly, based upon linear viscoelastic constitutive equation, the viscoelastic behaviour of viscoelastic Poisson ratio, bulk relaxation modulus and stress relaxation modulus of the grain and the interconversion of these parameters are studied. By given material data, using Prony Series, the primary curve of the stress relaxation modulus of the grain is obtained. According to axially natural period, the relation of the dynamic magnification factor vs the linearly loading time under linearly loading is deduced and presented.The essay has analyzed the structural integrity of the grain under axially high overload ,and the viscoelastic dynamic response of the grain is successfully simulated using large-scale computation software ANSYS. Adopting the results of Failure Tree Analysis of the motor and according to the primary influencing factors, the article has analyzed the free-filling grain under axially loading , has studied the grain with outer surface fixed to the case under axially loading at high