Taking Ahmed body with flow control slot at special location of slanted surface for object, the mechanism and effect of steady blowing/suction methods belonging to active flow control concept were studied by using large eddy simulation that is proved accurate. Base on analysis of flow field data, the blowing control method results in fully separation on the slanted surface and enlarged recirculation zone around body with higher aerodynamic drag, although trailing vortex pair is eliminated. The suction control method eliminates and delays the production and development of spanwise vortices structure with lower aerodynamic drag, however trailing vortex pair remains unchanged.