Ultra-high pressure abrasive water jet (AWJ), as a non-explosive tunnel excava­tion method, is proposed to reduce the impact on surface resident and other envi­ronmentally sensitive areas. In this paper, we carried out multi-phase simulation analysis of AWJ flow field based on Euler model to optimize the operation parame­ters of the post-mixing AWJ under the dual constraints of jet velocity and abrasive consumption. The characteristics of sand mixing in the nozzle, the evolution of the flow field and abrasive consumption under ultra-high pressure were obtained and analyzed. Considering the joint constraints of jet velocity and abrasive con­sumption, the operation parameters were optimized and recommended for tunnel contour cutting. This study is expected to provide theoretical and engineering guid­ance for future application of high pressure AWJ non-explosive tunnel excavation.