Abstract: In order to improve the laser damage resistance of fused silica optical surfaces, the appearance of smoothed fused silica surface defect and the effect of wiping off etching contamination are researched on HF-based etching processes under ultrasonic. And the experimental parameters are determined with SEM microscopy and atomic force microscopy to record face appearance and with one pulse laser incidence to measure laser damage threshold. Results show that it is advantageous to use HF-based etching processes under ultrasonic to smooth the defected surfaces and wipe off micrometer contamination particles. By experimental measurement, the parameters of HF-based etching processes under ultrasonic are obtained for different kinds of fused silica optics. The present research is very important for improving laser damage resistance of fused silica.