Abstract: A small diameter pipeline internal welding robot has been designed to address the low efficiency, high labor intensity, safety risks, and high skill requirements of traditional manual welding methods for small diameter pipelines, which are difficult to meet the needs of modern engineering. The robot can autonomously move inside the pipeline and use precise mechanical structures to achieve high-quality automated welding. The robot mainly consists of a walking mechanism, a tensioning mechanism, a welding gun lifting mechanism, a welding gun rotation mechanism, a wire feeding mechanism, and an intelligent control system. Through the intelligent control system, various motor drive units are accurately controlled to achieve fully electric welding operations. Compared with existing external welding equipment, this internal welding robot can effectively avoid external environmental interference, improve welding stability, and is particularly suitable for space limited welding and difficult to use traditional welding. This design not only enhances the flexibility of automated welding, but also demonstrates the intelligent development trend of welding technology, providing technical support for oil and gas pipeline construction.