Abstract: The surface etching of diamond single crystal by MnO₂ at different holding time was studied in this paper. The surface morphology and etching mechanism of the etched diamond single crystal were characterized and analyzed by scanning electron microscope and Raman spectrum. In addition, the anisotropy etching of diamond was discussed. The results show that, when the mass ratio of diamond to MnO₂ is 1:5, the etching degree of diamond single crystal increases with the prolongation of holding time, and the etching of 111 face is more serious than that of 100 face at the same holding time. The morphology of the etched diamond surface is related to the arrangement of carbon atoms on the corresponding crystal faces, so the etching pits of the 111 face are approximate triangular, while the etching pits of the 100 face are more quadrilateral. Furthermore, the compressive strength of the etched diamond single crystal decreases with the prolongation of etching time. The etching mechanism of diamond single crystal by MnO₂ is demonstrated that MnO₂ reacts with C atoms on the diamond surface to make the diamond surface etched.