This paper first outlines the worldwide oil and gas pipeline laying situation by 2013 and industrial applications, the working characteristics and advantages of orbital pipe welding robots using the gas metal arc metal(GMAW). Then the classifications of commonly used welding seam tracking sensors are comprehensively introduced. The sensor working principles, advantages and disadvantages and the application situation in pipeline welding are analysed in details. The studies show that arc sensors and visual sensors have many advantages such as good real-time characteristic, informativeness and high tracking precision, and are most widely used in pipeline welding. Using single sensor in different process can limit the tracking precision easily, but a system with multiple sensors will greatly improve the tracking precision in oil and gas pipeline welding. A system using visual sensor and arc sensor has been used in the gas field pipeline welding in Japan and a good effect has been achieved. Finally the conclusion is drawn that suitable seam tracking sensor should be chosen according to the process features and methods, and using a variety of sensors can improve the welding seam tracking precision, which will become the focus of future researches.