Abstract <p>This study investigated the carbothermal reduction etching behavior of the Fe₂O₃–C system on diamond (100) and (111) crystal planes at 1000°C. The results indicate that Fe and FeO, generated from the reduction of Fe₂O₃ by carbon, serve as the primary active agents for etching. However, significant differences in the etching mechanisms were observed between the two crystal planes. On the (111) plane, step-preferred etching led to the formation of triangular pyramidal pits, with the extent of etching diminishing as the carbon content increased. In contrast, the (100) plane exhibited square-shaped etch pits, and higher carbon content promoted deeper etching. This research elucidates the regulatory mechanism of anisotropic etching and raw material composition on etch morphology, providing a theoretical foundation for controlled etching processing of diamond.</p>