Abstract: In order to solve the low machining efficiency of polygonal shaft parts, a polygonal cross-section turning method was proposed. Firstly, a mathematical model of the tool axis and spindle motion was established, and the composite motion trajectory equation of the tool tip relative to the workpiece was derived. The effects of the rotational speed ratio and phase angle between the tool axis and the spindle on the target contour were analyzed. Subsequently, a motion control algorithm for the tool axis was proposed. A three-segment fourth-order displacement curve was employed during acceleration and deceleration phases to ensure smooth transitions between different spindle speeds. To tackle load fluctuations during the turning process, an adaptive interpolation algorithm based on a trapezoidal velocity profile was introduced. Additionally, a servo system tracking error compensation mechanism was proposed to resolve inconsistencies in cross-sectional phase angles caused by varying tracking errors. Finally, machining experiments were conducted on a CNC lathe. The results demonstrate that compared with milling, the proposed turning method increases efficiency by 63% in square-shaft machining while maintaining the required accuracy. Moreover, the method is applicable to shafts with different polygonal cross-sections, demonstrating the feasibility of the proposed method.