Abstract: Welding torch attitude identification is the necessary condition to realize automatic welding seam tracking and improve welding quality, which includes the detection of welding torch deviation and inclination.First a mathematical model of arc length is built, and then the character plane method is presented. Based on the three-dimension information acquired by rotational arc sensor and the character plane built by least-square fitting method, the deviation and the inclination of welding torch are obtained through calculating the intersection line slope of the character plane with the coordinate plane.The experiment results show that measure error of inclination is approximately ±7.85°, and the error of deviation is approximately ±0.42 mm;both of them meet the needs of real welding project.