Abstract: In order to study the influence of unsteady flow in an internal weapons bay on the separation characteristics of the weapon release, the DES (detached-eddy simulation) method is combined with an unstructured overlapping grid technique, and a high-precision numerical simulation method for the weapon separation process is established. On this basis, the numerical method is first verified with typical examples of cavity flow and weapon separation. Then, both RANS (Reynolds-Averaged Navier-Stokes) and DES methods are used to explore the evolution of vortices in the process of internal weapon separation, and differences between the obtained flow structures are analyzed. The influence of flow structures of the embedded weapons bay on the missile separation characteristics is finally quantified. Results show that, in the separation process, high intensity vortex structures are concentrated at the trailing edge of the chamber. Meanwhile, the shear layer of the chamber is destroyed by the missile, and the aerodynamic torque in the pitch direction of the missile changes rapidly at the exit stage. Compared to the RANS result, the high-intensity small scale vortex structures captured by the DES method have a significant impact on the pressure distribution on the missile, resulting in a large difference in the pitch angle and pitch angular velocity at the late stage of separation. For this reason, DES method is more suitable for a detailed study of the separation characteristics of an internal weapons bay. The outcome of this study can provide guidance in the selection of simulation methods and safety strategies for embedded weapon separation.