Abstract: Reasonable matching and effective:control of various welding parameters is one of the problems in the aotomation of all-position welding process for circular seam of pipeline.Integrating the techniques of path teaching,parameters matching and parmneters control,the automatic control system of all-position welding process for circular seam of pipelineis developed in this paper.The working principle,system structure and software design are also introduced.According to the welding position,the system can automatically assign the welding parameters,such as welding current,arc voltage,welding speed,torch swing speed and width.By ad-justing wire feed rate and the torch height,the PID control of welding cur-rent and fuzzy control of arc length are realized.This system has also the functions of off-line programming,path teaching and remembering weld tracking.Applying this system to all-position welding process for circular seam of pipeline,the automatic control of tool weld,filled weld and cover weld are realized.Experiments show that the,practical value of welding parameters fit the preset value very well and the weld formation is satisfied.