When rough grinding the sapphire substrate, it is necessary to use abrasives with large particle and high hardness to shorten the time. Considering the weak flowability and suspension characteristics of large-particle abrasives, the distribution and motion patterns of abrasive particles during rough grinding were studied by monitoring the swing of the removal amount pointer. Research shows that the dynamic balance of the abrasive layer has a decisive impact on thickness uniformity and surface quality of the substrate, and the establishment of this balance depends on a dense and uniform initial abrasive layer. The supplementary abrasive during rough grinding could only maintain the existing balance and could not be remedied in an imbalanced situation. The work helps to improve the control level of rough grinding process and has certain enlightening significance for in-depth research on the movement of abrasive particles during the grinding process.