Abstract: In order to compare the surface etching of diamond monocrystal, diamond is etched directly in air or with MnO₂ at different temperatures. The etching degree on the surface of diamond monocrystal was characterized by surface morphology, etching area and compressive strength of diamond single particle. The results show that both MnO₂ and air can successfully etch the surface of synthetic diamond monocrystal. With the increasing of etching temperature, the etching of diamond single crystal by air and MnO₂ intensifies. At the same temperature, when using MnO₂ as an enchant, the {111} face is more heavily etched than the {100} one; while in air, the {100} face is more heavily etched than the {111} one. After etching, the morphology of the etched diamond {100} face tends to form quadrilateral pits, while the {111} face is easy to form inverted pyramid corrosion pits. In addition, MnO₂ can promote the etching of diamond surface by expanding the etching area and decreasing the temperature of the maximum etching rate, so the compressive strength of diamond monocrystal decreases greatly.