Abstract: The additive manufacturing of Q345 low carbon steel using bypass coupling triple-wire gas indirect arc welding (BCTW-GIA) is reported. The influence of bypass current variation on arc characteristics is studied by using high-speed imaging equipment, and the corresponding formimg characteristics of beads are observed. The results show that with the increase of bypass current, the gradual increases happen to the proportion of direct arc and the welding heat input, however the gradual decreases happen to the proportion of indirect arc and the contact angle of the beads. When the bypass current is 155 A, a single-pass welding bead with the best spreadability can be obtained under the premise of good forming surface. Based on this set of parameters, the straight wall can be acquired by single pass and multi-layer additive manufacturing with a deposition rate as high as 13.3 kg/h. The high cladding efficiency and low heat input of the additive manufacturing method are conducive to improving the microstructure of the additive samples and increasing the average hardness. The average hardnesses of the bottom, middle and top areas of the sample are 186.80, 172.44 and 176.04 HV, respectively.