In the single-point diamond-turning process of monocrystalline silicon, tool wear affects the processing quality and efficiency of optical elements. The physical wear morphology of the diamond tools was observed using a scanning electron microscope and metallographic microscopy. The results showed that the diamond tools exhibited wear in stages: the stage of edge crushing, the stage of chip accretion, and the stage of tool surface grooving. Furthermore, based on the thermal–chemical wear mechanism, the formation mechanism of microgroove wear on the diamond tools were determined through energy spectrum analysis and X-ray diffraction. Finally, using a mathematical model that relates the surface roughness of single crystal silicon to the turning distance of the diamond tools, a tool life model was established.