<p>The robotic welding of 3D complex trajectory fillet welds in medium-thick plates remains a challenging endeavor, particularly in regard to the geometric intricacy of the weld seam and the multi-angle variability of the weld seam trajectory. In the context of such complex weld seams, the capabilities of existing vision sensors may be constrained in terms of high-precision measurement and real-time feedback. In contrast, rotating arc sensing technology offers significant advantages in terms of real-time performance, robustness, and environmental adaptability. To address these issues, we propose a 3D weld tracking method for robotic GMAW welding based on rotating arc sensing. The method mainly proposes a welding torch spatial position recognition method for the welding torch to extract its spatial position information, followed by the application of a pattern recognition algorithm to locate and identify the inflection point of the 3D weld. Specifically, this study introduces a pattern recognition algorithm that utilizes torch tilt change information to develop a suitable weld seam tracking method and corresponding controllers tailored to various tilt characteristics. Finally, the 3D weld seam tracking test results show that the tracking method can accurately identify the position of the welding torch; the average error of the monitored tilt of the welding torch is 3.3°, with a standard deviation of 0.38°, and the average tracking error in the direction of the Y-axis and Z-axis welding trajectory does not exceed 0.27&#xa0;mm, satisfying the criteria for real-time welding of 3D complex trajectory weld seams. for real-time welding of 3D complex trajectory weld seams.</p>