Abstract: Expandable Profile Liner is a kind of special section tube which would have a large deformation with hydraulic differential pressure.The weld should have good mechanical properties because the tube string should remain sealed during expansion. In order to improve the performance of weld seam,a number of welding methods were adopted which include TIG bottom welding,arc welding or TIG consmetic welding,one-side welding with back formation and detailed welding process procedure. Horizontal and vertical alignment devices are manufactured for the workpiece on downhand and overhead welding position. For the purpose of avoiding the influence of weld defects on expansion performance,a digital X-ray imaging defect detection technology was used,which has the functions of defect type identification,location extraction and size measurement. The measurement accuracy is up to 0. 01 mm. The results of stretching and winding qualitative assessment are up to standard.The finite element method is used to simulate the expansion state of weld seam so as to verify whether the welding seam meets the requirements of application in wellbore. The simulation analysis shows that the stress is less than the strength of weld seam in expansion process. The weld seam shows excellent performance in laboratory test and field application. Four wells have been used in the field,and the success rate is100%.