4H-SiC single crystal is a typically difficult material to process. The density and depth of surface damage after grinding directly affect the quality and efficiency of subsequent polishing operations. Grinding using traditional cast iron discs always results in significant scratches, broken edges, and an unstable removal rate for SiC substrates. In this experiment, a polyurethane pad was used to reduce post-grinding scratches, improve post-grinding surface quality, and achieve precise grinding of SiC substrates. The grinding experiments were carried out by changing the particle size of diamond abrasives, the rotating speed of discs, and the pressure added to the carrier disc. Our results show that the removal rate of SiC substrates increases with the increase of the rotating speed of discs, and the corresponding surface roughness after grinding decreases first and then increases. The removal rate of the SiC substrate increases with the increase of the particle size of diamond abrasives, but the surface roughness continues to increase. As the pressure added to the carrier disc increases, both removal rate and surface roughness after grinding increase, however, the increasing rate for the former would decrease, and the increasing rate for the latter would increase. Based on the experiment results, the optimal grinding conditions are as follows: the mass ratio of diamond in the slurry is 3%, the particle size of diamond abrasives is 1 μm, the supply rate for slurry is 5 mL/min, the pressure added on the carrier disc is 47 kPa, and the rotating speed of the disc is 35 r/min. Under this condition, a removal rate of 0.7 μm/h and surface roughness after grinding of 24 nm are achieved.