Abstract: Aiming at the low efficiency of CAM-based NC programming for the hole rounding feature of aviation transmission shaft parts, a dedicated NC macro program and corresponding user interface are developed for the Siemens 840D CNC system. A specialized hole rounding tool is adopted, a parametric trajectory equation for structural features is established, and the tool path design is finalized. The developed multi-hole rounding NC macro program enables hole rounding of shaft parts with regularly distributed holes and arbitrary quantities. Based on the macro program, a matching user interface is developed using SinuTrain software, achieving the visualization and input of hole rounding parameters, thus enhancing operational convenience and accuracy. Simulation validation of the NC macro program is performed via VERICUT software, followed by application validation in the actual processing of transmission shaft parts at an aviation manufacturing enterprise. The results indicate an 86% efficiency improvement relative to the conventional hole rounding process. The hole rounding trajectory planning is rational with accurate parameter transmission, enabling multi-specification hole processing. Post-processing, the hole transitions are smooth without tool marks, overcutting, or undercutting issues. This study provides an efficient and reliable technical method for the hole rounding process of transmission shaft parts.