Abstract: In order to reduce the welding heat input of low carbon steel and optimize the welding deformation and other defects, the triple-wire indirect arc welding (TW-GIA welding) method was used, and the heat transfer mechanism of TW-GIA was discussed based on the infrared temperature measurement system and high-speed imaging measurement results. The results show that TW-GIA welding has a significant advantage of small heat input, and can realize single-pass welding without obvious welding deformation. The width of the heat affected zone was smaller than that of MIG welding. Unlike traditional arc welding, the heat input of TW-GIA welding gradually decrease with the increase of welding height. Heat transfer mode changed from arc heat convection + molten pool heat conduction to only molten pool heat conduction when the welding height increased from 4 mm to 24 mm. The grain size of TW-GIA fusion zone and heat affect zone was small, and the widmannstatten structure was eliminated. The average microhardness of TW-GIA weld zone reached 289.8 HV, the maximum tensile strength was 472 MPa, and the elongation was 26.5%.