Abstract: Transonic buffet has a negative impact on the structural strength and fatigue life of aircraft, which may lead to flight accidents. For stationary airfoils, transonic buffet characteristics are associated with the freestream conditions, namely, the Mach number, angle of attack and Reynolds number. In this paper, a coupled method is established based on Unsteady Reynolds Averaged Navier-Stokes (URANS), and the effect of the elastic characteristics on buffet onset boundary is studied by releasing the pitching degree of freedom to serve as a variable quantity. It is discovered that the structure natural frequency has a great influence on the buffet onset boundary of the spring suspended airfoil, the system becoming unstable at a smaller angle of attack, while the mass ratio has a weak impact. The buffet onset boundary of the spring suspended airfoil is 1 degree less than that of the rigid stationary airfoil, making the elastic characteristics of the airfoil an important factor in transonic buffet studies.