Abstract: In the construction of oil and gas transmission pipelines, welding of steel pipelines with unequal wall thickness are common. The traditional fillet inner groove girth weld exists adverse effects such as root stress concentration, weld toe defects and miss test can realize equal wall thickness welding for connection of unequal wall thickness. Focusing on the PAUT test commonly used in oil and gas pipelines, in this paper, theoretical (simulation) analysis on the test quality problems caused by the conical inner groove was carried out, design and machining of the test block with different positions of defects was achieved, simulation and comparative analysis on this block was investigated. Finally, the appropriate minimum conical hole length was determined for providing strong technical support for engineering applications.