In order to improve the processing quality of ultraviolet (UV) nanosecond solid-state laser cutting polydimethylsiloxane (PDMS), a new method of mask-assisted laser cutting PDMS was proposed in this paper. Using polyimide film as the mask material, the process experiments of cutting PDMS with UV nanosecond solid-state laser without mask and with different thickness masks were carried out. The formation mechanism of microcracks on the surface of PDMS material was analyzed, and the influence of main laser process parameters on the groove depth, groove width, and processing quality of microgrooves was obtained. The results show that the surface quality of laser cutting PDMS under mask condition is good, no microcrack is generated and the glass transition is less. The groove depth and width increase with the increase of laser pulse energy and scanning speed. When the mask thickness is 15 μm and 50 μm, the scanning speed is 40 μm/s and 50 μm/s, and the pulse energy is higher than 0.40 mJ, respectively, and the heat-affected zone of the microgroove surface is small. This study provides a new method for improving the processing quality of UV nanosecond solid-state laser cutting PDMS.