In this paper, we introduce a numerical approach based on an unsteady aerodynamic model to study the dynamic stability of insect-like flapping-wing micro air vehicles (FWMAVs). Trimmed free flight of FWMAVs is simulated by a framework that couples the unsteady potential-based aerodynamic model and a multibody dynamics code. Flight dynamic modal structures are obtained by a linearization method. This paper also briefly presents the applications of the abovementioned approach to study several problems associated with the flight dynamic stability of FWMAVs, such as the effects of body aerodynamics and wing flexibility, as well as the ground effect.