Large-eddy simulation of a separated flow over NACA0015 at Reynolds number 1,600,000 at angle of attack 20.11 deg. is conducted to clarify the features of turbulent separated flow at high Reynolds number. The total number of grid point is approximately one billion, and a high order scheme is used in this computation. The LES result agrees with the experimental result in terms of the locations of the laminar-separation, turbulent reattachment, and the turbulent separation, and of the surface pressure distribution. The laminar-separation bubble is formed near the leading edge with turbulent transition. Then turbulent boundary layer develops over the airfoil surface and the flow is separated as a turbulent flow. The time-frequency analysis indicates there are two characteristic frequencies: 1)Strouhal number St = 100 at the turbulent reattachment point, 2)St = 4 at the turbulent separation point. These frequencies are expected as effective excitation frequencies to control the separated flow.