Abstract: Combining HF etching and differential interference contrast microscopy, this paper directly observes and analyzes the subsurface damages in fused silica optics. It is proved that the differential interference contrast microscopy has higher resolution than bright field microscopy and could detect the shallow scratches and dots. It is also revealed that polishing process would introduce lots of subsurface damages which are always covered by the redeposition layer. Most of the subsurface damages are plastic deformation induced shallow scratches and dots. A few fracture induced deep scratches and pits also exist. It is deduced that larger polishing particles incline to create severer and more subsurface damages.