The simulation of a separation control using a synthetic jet around an NACA0015 airfoil at Reynolds number 63,000 is conducted by a large-eddy simulation (LES) with a compact difference scheme. The synthetic jet is installed at a leading edge and actuated with nondimensional frequencies F+ = 1:0 and 6:0, which is numerically modeled by a threedimensional deforming cavity: "Cavity model" and a two-dimensional boundary condition on the airfoil: " Bc model". The aerodynamic coefficients of the controlled flows are similarly recovered from those of the separated flow using both of the Cavity and Bc model. However, the time-averaged values and flow fields are significantly different in two models, and the use of Bc model on the three-dimensional analysis is not proper. In the case with F+ = 6, a turbulent transition near the leading edge occurs much earlier with the Cavity model than the Bc model. This result indicates that the spanwise disturbance from the cavity to the separated shear layer should be carefully considered when three-dimensional unsteady analysis is conducted by LES.