A non-destructive technique for subsurface measurements is proposed by combining light scattering method with laser confocal scanning tomography. The depth and distribution of subsurface defect layers are represented in term of scattered light intensity pattern, and three types of fused silica specimens are fabricated by different grinding and polishing processes to verify the validity and effectiveness. By using the direct measurement method with such technique, micron-scale cracks and scratches can be easily distinguished, and the instructional subsurface defect depths of 55, 15, and 4 \mu m are given in real time allowing for an in-process observation and detection.