Abstract: This work analyses the structural integrality for a large aspect ratio dual thrust solid rocket motor (SRM) grain of one antiaircraft missile. Various loading conditions were analyzed during spinning launching process. Based on 3D viscoelastic FEM method, the stress-strain fields were simulated. Results show that the interior pressure loads, axial inertial loads and angular acceleration loads are the primary loading factors that influence its structural integrity. The rear face of grain boss is the dangerous place and the excessive stretch of the cantilever section would lead to gas channel's congestion, which might cause the interior pressure drastic-increasing even failure of shell. It is suggested that the following measures be effective to optimize the structure of solid rocket motor, such as improving the charging tooling to avoid micro-crack, setting the fixtures or supporting mechanism to cantilever section and optimizing the ratio of burning surface to port area ratio.