Abstract: Safe and stable separation process of a missile from an aircraft is very important for both the flight stability of the missile and the safety of the aircraft. To study the aerodynamic interference between the missile and aircraft, and the flight trajectory of the missile during the ejecting process, numerical simulation of the separating process of a typical air-to-air missile with high length-to-diameter ratio is carried out with two types of numerical methods, that is, the rigid body six degree of freedom (6DOF) method and the computational fluid dynamics/computational structure dynamics (CFD/CSD) two-way coupling method. The rigid body 6DOF method is based on the coupling of the governing equations of fluid dynamics and the 6DOF exterior ballistic code, and the CFD/CSD two-way coupling method includes the coupling of the governing equations of fluid dynamics and the structural dynamics equations. The aerodynamic characteristics and variations of the flow fields are obtained by these two different methods. The time histories of aerodynamic coefficients and the trajectory parameters are displayed. Their similarities and differences are compared and analyzed. Furthermore, the influence of the elastic deformation of the missile structure on the separating movement is discussed.