Taking the classic wing pylon finned store model for example, the overset grid system and CFD (computational fluid dynamics) technology were utilized to study the aerodynamic interference characteristics of the external store separation from two aspects:the interference condition simplification and the analysis of factors influencing aerodynamic interference characteristics. The predicted results of missile separation trajectory parameters and aerodynamic interference coefficients coincide well with the CTS(captive trajectory system) results, which indicates that the proposed computing method can effectively predict the separation trajectory and complex aerodynamic interference between the missile and aircraft. Based on the results of CFD numerical simulations, the missile aerodynamic interference law of separation can be obtained for different working conditions of mach number, wing angle of attack, missile angle of attack and so on. Furthermore, the incremental coefficient method with first-order heterodyne processing is also obtained to give aerodynamic interference data for the defect working condition. The proposed method can be utilized to predict the separation trajectory and to design the aerodynamic interference characteristics between the missile and aircraft, thus producing great values in practical engineering applications. 