Abstract: Based on the notch width of plasma cutting quality evaluation standard, the cutting depth was introduced, and the notch depth-width ratio was proposed as the quality evaluation parameter of plasma air gouging. Taking nozzle aperture, cutting torch angle, current intensity and air gouging speed as design variables and depth-width ratio as target response value, the cutting experiment of Q345B steel plate was carried out by response surface method. The mathematical optimization model of cutting process parameters on the depth-width ratio was established, and the influence of air gouging parameters on the depth-width ratio was analyzed. The optimized cutting parameters were obtained, and the plasma air planing test of the pipe was carried out to verify the results. The results show that when cutting 20 mm thick Q345B steel plate, the process parameters of plasma air gouging are adjusted as follows:nozzle aperture of 4 mm, cutting torch angle of 44°, current intensity of 190 A, air gouging speed of 735 mm/min, the cutting efficiency and cutting quality are the best, meanwhile, the maximum cut depth-width ratio is 84.8%. Compared with carbon arc gas gouging cutting pipe, the pipe surface after plasma gas gouging cutting needn't secondary processing, the cutting efficiency is increased by 64.24%, which provides a new technical way for the rapid and efficient cutting operation of underground channel new pipe curtain method.