The computer numerical control system for pipe connecting trace processing was researched and developed by means of industrial computer and system integrated technology in this paper. According to the regularity of the pipe connecting trace, a general mathematic model was established to process column pipe connecting traces with several pipes intersecting at any angle. Then the composite locomotion forming the connecting trace was decomposed into the rotation of the pipe and the horizontal movement of the welding torch. Finally, the distance of the two partial movements was converted into the number of pulses and these pulses were sent out by stepping motor card to drive the two stepping motors. The dynamic data exchange (DDE) technology and multithreading technology are adopted to enhance the performance of the system.