Abstract: Based on the investigation of the relationship between the are voltage and the are length in small current pulse TIG welding, a new are length sensing and control method has been put forward and realized with hardware circuits. Then, an arc length tracing system has been established. The experimental results proved that the are length could be controlled over a larger current range both in the pulse TIG welding and in the DC TIG welding.When the average current is 20A and the given tracing length is 1 mm, the static are le ngth tracing error is ±0.1 mm. The developed system has high control accuracy, fast dynamic response, high operation reliability. Adopting this method, the arc length tracing problem, which exists in welding processes of thin stainless components with complicated curved surface, has been solved successfully, while such problem couldn't be satisfactorily solved by the conventional arc length tracing methods.