In the present study, a numerical study about flow control of a wind turbine airfoil was performed using computational fluid dynamics (CFD). Two dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) solver was used to solve the flow around a wind turbine airfoil. Synthetic jets were applied to the DU 35 airfoil used in the inboard section of the NREL 5MW wind turbine. In order to simulate the synthetic jets, suction/blowing boundary condition was applied. The flow characteristics of synthetic jets were investigated according to the injection speed and injection angle. The injection velocity is 1, 2, and 3 times the freestream and the injection angle is 45 degrees. As the injection speed increases, more energy is transferred into the boundary layer. Therefore, the performance of the DU 35 airfoil is most improved when the injection speed is 3 times the freestream. In the case of the injection angle, the flow analysis was performed at 0 degrees, 45 degrees, and the direction perpendicular to the surface. The injection speed at this time is 3 times. The size and shape of the vortices generated by the synthetic jets depend on the injection angle. When the injection angle is 45 degrees, the performance enhancement of the DU 35 airfoil is the greatest.