Abstract: ERNiCr-3 nickel-based alloy welding material was overlaid on the low alloy steel T23, and the macrosegregation characteristics and the formation mechanism in the welded joint were investigated.The structure of the welding interface after overlay welding was characterized by optical microscope (OM), scanning electron microscope(SEM)and electron backscatter diffraction (EBSD).The results show that macrosegregation mainly occurs at the overlapping region of weld beads, a band structure in the weld metal near the fusion line is formed with high Fe content and same crystal structure with the low alloy steel base metal.The formation of macrosegregation is mainly related to the liquidus temperature difference between the base metal and the filler material.Because the liquidus temperature of nickel-based filler material is lower than that of the low alloy steel base metal, the temperature of local molten pool at the overlapping region of weld beads is lower than the liquidus temperature of base metal.Hence, the molten base metal flows into the region by convection will quickly solidify due to undercooling, resulting in macrosegregation.Selecting filler material with similar liquidus temperature to that of the base metal and reducing the welding heat input will help to reduce the macrosegregation.