In the case of a aircraft wing with external store, the mass and location of the external store can largely affect the dynamic stability and controllability. It is important problem to choose the proper location and to design the mechanism of pylon carrying auxiliary fuel tank, bomb or missile. A well-designed decoupler pylon can minimize dynamic instability of a wing structure. In this study, it has been demonstrated the effect of passive flutter suppression technique using the decoupler pylon model. CFD-based TSD code is used to calculate three-dimensional unsteady aerodynamics, and finite element method is applied to the free vibration analysis of the wing-pylon-store structure. The flutter boundaries of the clean wing and wing with decoupler pylon/store are compared in this paper. Also, the effects of structural parameters of decoupler pylon have been studied.