With the method of mask projection and direct-writing etching on the front surface of silica glass by a 248 nm nanosecond excimer laser, the influence laws of laser pulse energy density, repetition frequency, scanning times on micro-groove cracks are studied, and the mechanisms of laser etching and cracking of silica glass are analyzed. The results show that the mechanism of silica glass etched by a 248 nm nanosecond pulse excimer laser is the joint effects of photoionization and thermal ablation. The laser energy density threshold range for the crack-free etching of JGS1 silica glass is 16-30 J·cm-2 and the etching rate can be up to 500 nm per pulse. With the increase of laser repetition frequency and scanning times, the micro-grooves are easily cracked because of the heat accumulation and plasma micro-explosion shocking. Based on the optimized laser processing parameters, when the width of micro-grooves is less than 100 μm, the processing of crack-free linear-type (the depth is less than or equal to 50 μm) and circular-arc-type (the depth is less than or equal to 28.5 μm) micro-grooves can be achieved.