Performing grinding before polishing is a widely used method of realizing large silicon wafers with high flatness. The variations in the size of the abrasive grains of a grinding wheel affect the surface quality of a ground wafer. We propose a simulation-based approach for analyzing the effect of the variations in grain size on surface quality. Rapid and accurate geometric simulation of the wafer grinding process is a key technology of the analysis. In this paper, we propose a novel method for simulating infeed grinding. Grinding is simulated with many abrasive grains of different sizes by executing geometric milling simulations with micro ball-end cutters of various radii. The polygon rendering hardware of a graphics processing unit is used to accelerate the simulations.