The material removal mechanism in the chemical–mechanical polishing (CMP) process is closely related to the tribochemical reactions. In order to understand the tribochemical behaviors of diamond polishing SiC in different environments, the polishing processes in dry, pure water, and H2O2 solution are studied by the reactive force field molecular dynamics (ReaxFF-MD) simulation. Three types of chemisorption, -H, –OH, and -O-, are found on the surface of SiC in both pure water and H2O2 solution. Besides, three different material removal methods are summarized in the CMP process of SiC with diamond abrasives, namely mechanical removal, adhesive removal, and oxidative removal. Although there is oxidative removal in water and H2O2 solution, the total atoms removed will actually decrease, because the chemisorption reduces the atoms removed by adhesive removal. It is found that H2O2 solution can more effectively reduce adhesive bonds and is more conducive to oxidative removal. The reduction of adhesive bonds and changes in material removal methods result in a smaller average friction coefficient and less structural damage during polishing in H2O2 solution. This study reveals the relationship between material removal and tribochemical reactions, which can provide some guidance for the improvement of CMP process.