Abstract: This paper presented a PMAC-based automatic welding machine which could accomplish welding of intersection line seams of anellipsoidal end and a pipe at even speed while real-time motion control for welding piece and welding torch is implemented by PMAC(programmable multi-axes controller).The welding machine structure and its components,the intersection line seanlmodeling,the control of instantaneous angular velocity of the rotating welding piece as well as the speed control of welding torch were discussed.Elementary experiment results showed that the welding machine had high working efficiency and stable welding quality,and could ensure a、smooth welding surface.