Abstract: In order to investigate the micromechanism of high/ultrahigh speed grinding process with single CBN grain, the mechanism of CBN abrasive grinding high-speed steel SHK-9under different process parameters was studied by using Lagrangian/Euler fluid-solid coupling method with random shaped CBN abrasive as the analysis model.Result shows that the tangential grinding force of CBN abrasive grains sized 124 to 150 μm is maximized at cutting depth of 20 μm or 30 μm, cutting speed of 120m/s, but it is minimized at cutting depth of 40 μm.With reduced grain size of CBN abrasive, the grinding force decreases obviously, while abrasive grains can form narrower scratches on the surface of the workpiece.Therefore, the appropriate grinding depth combined with proper grain size can improve the grinding surface quality.