Single-crystal SiC has been widely applied for electronic devices. Photocatalysis assisted chemical mechanical polishing (PCMP) is an efficient global flattening technology for finishing SiC, but the atomic level removal mechanism is still under discussion. In this paper, the atomic behavior of removal with hydroxyl free radical (·OH) aqueous solution was investigated using the ReaxFF molecular dynamics (MD) simulation. The theoretical analysis shows that ·OH oxidation of SiC can occur spontaneously, and the mechanical behavior would be able to increase the potential energy and reduce the reaction barrier the reactants. The simulation results show that with only chemical oxidation occurs, the SiC surface adsorbed O, H or -OH to produce Si-O*H2, Si-OH2, Si-OH, Si-H2O, Si-H*O*-H2O, Si-H2O*, Si-O*H* and Si-H, etc, no Si atoms were observed to detach from the SiC substrate. Nevertheless, if the mechanical action was applied, some Si and C atoms break off the substrate by forming SiO, SiO2, CO, CO2 or chain, and the other Si or C atoms were detached by the adsorption on the abrasive. In addition, no atoms break away from the substrate in H2O solution. The force F x in H2O solution is less than that in ·OH aqueous solution because of the lubrication of H2O solution. Furthermore, it is found that the mechanical action applied, the more -H and -O adsorbed on the SiC surface result in the more Si and C atoms are removed. The experimental results show that SiC wafer could be oxidized by ·OH under the mechanical action of diamond abrasive particles. This study reveals that the removal of Si and C atoms from the substrate is the result of the combined action of chemical oxidation and mechanical sliding, which is helpful to explain the dynamic process of the oxidation and removal of Si and C atoms on the atomic level in the SiC PCMP. Furthermore, it provides a valuable method reveal the material removal mechanism.