Abstract: The characteristics of welding current was investigated in terms of waveform, statistical characteristic, self-correlation and cross-correlation of the welding current in the process of tandem twin-wire welding with rotating arc. It showed that the welding current on the front wire are fluctuating with an approximate sine wave, due to the varying tip-to-workpiece distance with arc rotating. Based on the analysis of welding currents and voltages, it is found that the self-correlation factors of the welding current of the front wire apparently increased with the increasing of idling weld current, which means that the increase of weld current is helpful to improve the sensitivity of rotating arc sensor. However, the influence between the two wires was increased with the increase of welding current. With the increase of weld voltage, the stiffness of arc was increased and the fluctuation of welding currents in the leading wire decrease, which lead to the decrease of sensitivity of rotating arc. A soft threshold wavelet filter algorithm and a segment parameter self-turning fuzzy control method was developed, the curved fillet weld seam tracking was achieved successfully under the welding speed of 90 cm/min.