Abstract: In order to study the effects of CO2 laser pretreatment parameters on surface roughness of fused silica, the fused silica samples were irradiated by a 100 Hz CO2 laser with a spot size of 1 mm2. Repairing degrees were defined as mild, moderate and severe. Surface roughnesses under different repairing degrees were statistically studied. Besides, surface roughness was investigated for the samples after single shot irradiation by CO2 laser at different pulse durations and duty cycles. The results show that the sample’s surface roughness and crater depth increase with the increasing duration and duty cycle. The rate of increase rises gradually as the duration increases, while descends gradually as the duty cycle increases.