Abstract: An automatic arc welding machine for making pipe seam in revolving ellipsoid end of vessels was designd and its structure, components, and working principle are discribed in this paper.The equations for calculating the geometry and dimensions of the cams was deduced, which are the key prats to control the moving locus of arc welding torchs. The welding machine has been successfully applied to the automatic welding production of boiler cylinders with revolving ellipsoid end. The production practice has shown that this automatic welding machine is suitable for the intersection-line seam in revolving ellipsoid of end boiler cylinders and has a good results. It is a new all-purpose type of low cost automatic welding equipment for intersection-line seam.