Abstract: The lightweight thin-walled stiffened structure composed of skeletons and skins is mostly applied in the wings and bodies of high-speed flight vehicles. When the vehicles are flying at transonic or low-supersonic speed for a long time, this thin-walled structure will show strong nonlinear fluid-solid coupling characteristics under unsteady aerodynamic loads. Among them, the nonlinear interaction between fluid nonlinearity such as shock-wave movement, boundary layer effect, flow separation and geometric large deformation will cause the unstable behavior of the panel, thusly result in structural fatigue or damage. Based on CFD/CSD coupling method, this paper predicts and discriminates the response of the panel in the transonic domain with Mach number. It is found that single-mode flutter occurs in the transonic regime, and there will be the convergence, first-mode LCO, buckling, transonic flutter, non-resonant LCO, resonant LCO, high-frequency periodic oscillation, high-frequency non-periodic oscillation, and so on for the shape evolvements with the Mach number. The evolution pattern changes when the thickness of the panel increases, and the incoming flow density decreases. Furthermore, there will be a delay and damping effect, which can suppress the high-frequency non-periodic oscillation when considering the unsteady acceleration and viscous effects. It has a positive effect on reducing the fatigue damage of the structure.