Abstract:  To address the issues of poor size adaptability and low clamping efficiency in traditional welding positioners during pipe flange welding, this study proposes a structural design scheme for an adjustable pipe flange welding positioner. By integrating a mobile base, track system, and pneumatic three-jaw chuck through modular design, the distance between the driving end and driven end is flexibly adjusted to accommodate pipelines of different lengths. Adjustable roller supports combined with pneumatic clamping enhance automation. Structural reliability was verified via modeling in Creo Parametric and static mechanics analysis in Creo Simulate. Under two typical working conditions, the maximum stresses were 73.05 MPa and 104.1 MPa, respectively, both below the yield strength of 45 steel (355 MPa), with safety factors exceeding 2.5. The maximum displacements were 0.375 mm and 0.19186 mm, meeting positioning accuracy requirements (<0.5 mm). The design improves welding efficiency through modular and automated design, reduces fixture requirements and maintenance costs, and demonstrates potential applications in petrochemical, nuclear power, and related fields.