Abstract: In this work, ER120S-G/SS316L bimetallic steel (BS) were fabricated via dual-robot collaborative CMT wire arc additive manufacturing combined with an alternating linear deposition strategy. The microstructure, element distribution, phase composition and mechanical properties of specimens were systematically analyzed by SEM, EDS, XRD, micro Vickers hardness tester and electronic universal testing machine. The results show that no macroscopic cracks or delamination defects are observed at the BS interface. The effective interdiffusion distance of elements is approximately 32 μm, forming a continuous compositional gradient layer. The interface is mainly composed of austenite and acicular martensite. The ER120S-G region consists of lath martensite, while the SS316L region is dominated by austenite with a small amount of delta ferrite. Carbon enrichment at the interface induces carbide precipitation, and the maximum hardness reaches 416.5 HV. A continuous hardness gradient zone of 7–8 mm is formed extending from the interface to the ER120S-G matrix. Bidirectional tensile tests reveal that the ultimate tensile strength of the specimens in X and Y directions is 839.2 MPa and 821 MPa respectively. The specimens exhibit slight mechanical anisotropy, and the fracture mode is dominated by dimple-type ductile fracture, presenting excellent overall plasticity and load-bearing capacity.