Abstract: With high speed camcorder system and digital oscillogragh, the electic arc shape of twin-wire indirect arc welding was investigated.Results show that the arc was burning between the two wires in twin-wire indirect arcwelding, and the arcwas still a type of gas discharge in nature.Welding current, arc voltage and the distance between the two wires and the workpiece have great influence on the arc shape.With the welding current changing, the arc shape presents different degree of concentration and scatter.The arc becomes brighter and biggerwith the increase of arc volgage. Whenthe distance between the two wires and the workpiece reduced, the arc concentrated and became shorter and brighter.Arc voltage changes periodically, and its corresponding electric arc shape changes also periodically, and it has well corresponding relationship between arc voltage and electric arc shape.