The 2-D time-dependent compressible Navier-Stokes equations are adopted as the governing equations. The unsteady lift coefficients of airfoil are calculated by Navier-Stokes equations with the implicit LU-NND algorithm, Baldwin-Lomax turbulent model and C-type grids. The fluctuating values of lift coefficient are increased with the enlargement of incidence and Mach number. The buffet onset boundary is defined as the beginning point where the fluctuating values of aerodynamic coefficients are increased suddenly. The fluctuating values of aerodynamic coefficients expresses the buffet strength. The buffet characteristics of supercritical airfoil DFVLR-R2 and airfoil NACA0012 are investigated. The calculating results show that:in the design Mach number range of supercritical airfoil, there are larger buffet onset incidence and less buffet loads. When Mach number is larger than the design Mach number, the buffet onset incidence of supercritical airfoil decreases quickly and there are rather large buffet loads. In the convention airfoil NACA 0012, there are much less buffet onset incidence, larger buffet loads and separated range.