Abstract: A bypass-coupled three-wire indirect arc additive manufacturing process was adopted to simultaneously melt two dissimilar wires, namely ER50-6 low-alloy steel wire and ER316L stainless steel wire, to fabricate single-track multi-layer wall components of low-alloy high-strength steel. The arc morphology and metal transfer mode during the synchronized feeding of three wires were systematically investigated. Welding parameters were monitored and adjusted via an automatic wire feeding system to improve the forming accuracy and performance of the workpiece, and the strengthening mechanism of the mechanical properties of the additively manufactured components was explored. Experimental results indicate that when the welding current is 320 A; the welding height is 3 mm; the main wire feeding speed is 6.5 m/min; the side wire feeding speed is 5 m/min, and the welding speed is 8 mm/s, the wall surface is smooth; the forming accuracy is optimal; the metal deposition efficiency reaches 11.4 kg/h. During the rapid cooling process of the molten pool, the supercooled transformation of austenite occurs, accompanied by martensitic transformation and bainitic transformation. The multiphase microstructure synergistically improves the component performance. The average tensile strength of the components reaches 1 035 MPa; the elongation after fracture reaches 26%; the average micro Vickers hardness is 380 HV. All properties are in the qualified range of low-alloy high-strength steel. This process provides a novel and feasible idea for high-efficiency and high-performance arc additive manufacturing of low-alloy high-strength steel.