In this work, the pits were successfully etched on the (001) sapphire single crystal surface. The experiments were processed by using fused KOH etchant at different temperature about 15 minutes. The difference in the morphology of etching pits on c plane sapphire was observed by metallurgical microscope and atomic force microscopy. It was found that the size of etch pits would be increasing if the temperature high enough. And the density of etch pits had a maximum at about 320°C.Finally, it was put forward and discussed that three kinds of mechanisms about the etching pits based on the experimental fact: annexed, merger, expansion.