Abstract: The arc sensor detects the weld seam position based on the change of welding arc signal, and it doesn't need no additional devices and has advantage of low cost. But the low sensing accuracy and stability has limited its application. From the aspect of engineering application, the factors in welding system influencing arc sensing accuracy were studied. It is found out that the position signal from the actuator, the arc interruption, the groove angle and the data extraction method play an important influence on the sensing accuracy and stability. Solutions were given out for each factor. The research has certain guidance for improving the arc sensing accuracy and stability in engineering application.