A nondestructive detection method of subsurface damage depth was proposed, in which nano-fluorescent quantum dots were added as marker in grinding and polishing process, and the quantum dots were excited by light and produced fluorescence, then the slice images of the samples at different depths were obtained by laser confocal microscopy. When the scanning depth reached a certain value, the fluorescence intensity became weak and the subsurface damage depth was determined by fluorescence intensity change of the feature points. A nondestructive detection software of subsurface damage depth, which has functions of image threshold processing, bright spot automatic recognition, image display and curve characterization, is developed and it can realize the rapid detection of subsurface damage depth. The results of non-destructive detection and damage detection were compared, and it showed that the relative error between the two detection methods was less than 10%, which verified the effectiveness of the proposed method.