Abstract: The friction taper plug welding（ FTPW） device designed by Tianjin University was used to study the influence of axial offset distance of plug from the center of hole（ namely different concentricity） on the weld quality. The morphology of the bottom corner of the weld joints was observed and analyzed,and the joint quality obtained by different geometry and concentricity of the hole and plug was compared and analyzed. The results showed that no qualified welded joints could be obtained at all by different axial offset distances under the condition of the geometry A with less contact area and narrower gap,and that the defects of one side with larger gap were worse after the plug being offset. For the geometry B with larger contact area and larger gap,there were minor defects and the overall quality was okay when the offset distance was zero. The concentricity between plug and hole should be controlled within ±0. 5 mm.