Abstract: In order to optimize the surface performance of Q345 low carbon steel and reduce the dilution effect of substrate on Ni-based fusion layer, three groups of nickel-based metal powder-cored wires with different Fe content were designed, and three kinds of transition layer+Inconel 625 fusion layer were prepared by TIG deposition method. The microstructure, element distribution, phase composition, interface element diffusion and surface hardness of the fusion layer were studied by OM, SEM, EDS and microhardness test, which provided theoretical support for the popularization and application of gradient Ni-based fusion layer. The results show that under the influence of solidification temperature, the melted coating layer forms different grain morphologies from the interface to the top. The coating is mainly composed of FCC structure γ-Ni matrix, Laves phase and MC phase. Due to the existence of microsegregation, the element distribution in the solid solution is not uniform, Ni, Cr and Fe are mainly enriched in the crystal, and Mo and Nb are gathered between the crystals. With the increase of Fe content, the degree of element segregation in the transition melting layer slows down, and the content of Laves phase with irregular shape decreases. Thanks to the solid solution strengthening and second-phase particle strengthening of alloy elements, the average hardness of Inconel 625 melted coating layer reaches above 200 HV0.2, and the hardness is slightly lower in the upper part of the transition layer due to the influence of repeated heat input. The microhardness of the fusion layer is higher than that of Q345 substrate.