To establish an effective and nondestructive subsurface defects detection technology, the fluorescence image technique of optics subsurface defect was studied. A small-aperture fluorescent defect-detection prototype was developed by systematically optimizing various parameters such as the excitation wavelength, imaging spectrum, imaging light path, and the detector. Based on the prototype, the surface and subsurface fluorescence defects of the finishing processing of fused silica and diamond fly-cutting processing KDP were characterized. The laser-induced damage threshold was measured by a 351-nm nanosecond pulsed laser. There is a significant difference in the subsurface defects of various samples, ranging from 0.012% to 1.1%. The relationship between the subsurface defects and the damage threshold was analyzed by statistical methods. The results show that the R2 value of the fused silica subsurface defect and the damage threshold curve is 0.907, and the R2 value of the KDP crystal subsurface defect and the damage threshold correlation curve is 0.947; both are strongly related. The results can be used to evaluate the processing quality of the optical components.Because of its nondestructive and short duration characteristics, the technique can be applied to the detection of full-area subsurface defects in large-dimension UV optical components, which makes it vital in engineering.