Abstract: To investigate the influence of blasthole spacing on the blasting contour quality of tunnels (overbreak and underbreak) and to address the fragmented workflow between blast design, model construction, and numerical simulation in conventional blasting analyses, a parametric blasthole layout–modeling–analysis method is proposed based on an explicit dynamic finite element program. A Fourier transform and an unsupervised K-means clustering algorithm are further employed to establish quantitative indices for blasting quality evaluation. The proposed method enables rapid adjustment of blasthole positions, automatic construction of three-dimensional numerical models, and quantitative analysis of simulation results, allowing the overall analysis workflow to be completed within 30 min. Based on the Yinggeling Tunnel project in Hainan, a total of 43 simulation cases were conducted to quantitatively analyze the effects of peripheral blasthole spacing, auxiliary blasthole spacing, and the cut zone range on the blasting contour formation quality of the surrounding rock. According to the optimized blasthole spacing design, the average tunnel overbreak was reduced from 17.1 cm to 10.2 cm, and the blasting quality was improved by approximately 30%.