Abstract: The thick carbon steel plates of 6 mm, 12 mm, 16 mm, 24 mm and 40 mm were welded by the deepen arc technology developed by panasonic of tangshan, and 3 kinds of T joints were welded. Test results show that, the depth of deepen arc technology is larger than that of ordinary gas arc welding, and under the proper welding process, the full penetration of T-joint can be achieved by reducing or no groove for the thick carbon steel plates under 16 mm. The welding effect of full penetration can be achieved by the welding of 24~40 mm carbon steel test plate with K-45° groove under proper welding process conditions, and the root cleaning treatment is not needed after welding. The deepen arc technology is suitable for bottom welding of thick plate carbon steel, and the penetration shape is finger-like depth, which is conducive to achieve full penetration of welding root.