Fused silica optic was etched by HF solution, the morphology and damage properties of micro subsurface cracks were studied, and factors increased crack damage properties were explored. Finite difference time domain algorithm was used to calculate light intensification in the vicinity of cracks. Calculation results show that light intensification caused by crack contained with ZrO2 particle (diameter 50 nm) is 6.1 times of the incident light, and the maximum intensity lies inside the crack and close to the particle. However the light intensification caused by crack with the same structure and without particles inside is 3.6 times of the incident light, and the maximum intensity lies outside the crack. By HF etching, contaminations in crack are eliminated, breath depth ratio of the crack is increased, and light intensification caused by the etched crack is only 2.2 times the incident light. Experimental results also indicate that damage threshold of deeply etched crack is increased by one time, and 1 064 nm absorption of it is only 230 ppm. Damage performance of crack free area is also improved by HF ethcing, but damage threshold of the crack free area does not increase as along as etching proess goes on. It begins to decrease after reaching a maximum value, thus etching process will terminate till damage threshold of the crack free area reaches its maximum value.