Abstract: Based on the large eddy simulation (LES) and combined with three-order WENO scheme and the immersed boundary method (IBM), the flows past a NACA0012 airfoil with and without a micro-ramp vortex generator have been simulated at the Mach number of Ma=0.5 and in an angle of attack α=10°, and different flow structures under these two cases have been compared. Our numerical results show that the micro-ramp can change wake structures, and can lead to the reduction of a boundary layer separation area, and an increase of lift. Furthermore, the suppression mechanism of the micro ramp on flow separation have been discussed.