In this paper, the surface damage mechanism of silicon carbide lapping process was studied. A theoretic model between the depth of subsurface damage and surface scratch of silicon carbide substrate double-side lapping has been built. An experiment of two-sided lapping combining VK-X100/X200 shape measurement laser microscopy system with HF mild chemical etching experiment on SiC substrate was processed to obtain the distribution of surface scratch and subsurface damage layer with depth. The study shows that the thickness of subsurface damage layer decreases as the depth increases, which centrally distributes in the depth of 0–15.6 μm from outer fragmentation and scratch damage layer, which accounted for about 98.6%. The result can help us to optimize processing parameters of silicon carbide substrate double-side lapping to control the depth of subsurface damage layer.