Scratches are commonly found defects in optical glasses, which degrade their beam quality, enhance the thermal effect, and reduce resistance to laser damage. Therefore, accurate detection and characterization of scratches is critical during processing. In this study, an optical glass with a scratch depth of 70 nm was selected as the detection sample. The optical glass scratch information was loaded by light waves using an optical interference method. Then the interference fringe image was processed and edge-detected, and finally the actual scratch depth value was obtained. Experimental results show that the relative error observed for the 70 nm scratch depth of optical glass using optical interferometry is less than 1%. Thus, the proposed method provides a detection method for the scratch depth value in the order of tens of nanometers during optical glass processing.