Abstract: Aiming at the problems that the bonding layer was easily aging and peeling, poor long-term stability, and weak environmental adaptability in traditional steel/lead bonding structures in the field of nuclear weapons equipment, a new arc additive manufacturing process of droplet deposition composite TIG was proposed to manufacture steel/lead bimetallic structures.Solidification morphology of lead alloy droplets after impacting and spreading on 45 steel cold substrate and molten pool on surface of 45 steel was comparatively studied in this paper.Effects of impact velocity and initial temperature of droplets on solidification morphology of the impacted droplets were investigated by adopting dimensionless numbers.Interfacial microstructure and Vickers microhardness of steel/lead bimetallic specimens were analyzed by methods of OM, LSCM, SEM, EDS, XRD and hardness experiments.The results showed that spreading factor of lead alloy accumulation layer increased nonlinearly with the increase of impact velocity of droplets.Intermetallic compounds of interface layer were mainly FeSb2 and FeSn2, whose thickness increased with the increase of arc heat input.Vickers microhardness at the interface of steel/lead was significantly greater than that of lead alloy accumulation layer and 45 steel base metal.Hardness on the left side of interface layer center reaches the maximum value 785.3 HV, average hardness of 45 steel was 343.7 HV, and average hardness of lead alloy was 24.3 HV.