Using excimer laser with 157 nm wavelength,experimental studies on micro-ablation of LED-GaN semiconductor films have been performed. The primary etching performance and mechanism of GaN-based semiconductor materials have been investigated and analyzed. The results show the etching rate above 50 nm/pulse can be achieved as the laser fluence is higher than 2.5 J/cm2. For 157 nm laser direct writing,the etched surface with roughness lower than 30 nm-Ra which can be obtained when the laser repetition rate is smaller than 16 Hz and the scanning velocity is higher than 0.25 mm/min. Using laser scanning approach for GaN film etching,a sidewall with about 75° sharpness can be fabricated. The potential of the 157 nm laser for micro-machining of three-dimensional (3D) micro-structures has been proven. Photo-chemical reaction induced by single photon absorption ionization plays a dominant role in GaN-based material etching with 157 nm laser.