The Inconel 625 nickel based alloy was deposited on 30CrMo steel substrate using hot wire TIG welding process. The effects of different preheating temperatures on the microstructure and properties of deposited joint and layer were analyzed and compared, in order to determine a reasonable hot wire TIG welding process. Research has shown that Inconel 625 nickel based alloy has a good bonding with 30CrMo steel base material, and there are no welding defects. The preheating temperature has little effect on the formation morphology, corrosion resistance, and joint bending performance of the overly layer. The bending performance of the base metal joint is good at all temperatures, and there is no cracking phenomenon. However it has a significant impact on the hardness of the heat affected zone and the fusion ratio of the overly layer. The microstructure of each temperature overly layer is dendritic austenite, transitioning from inside to outer into cellular, columnar, dendritic, and equiaxed crystals. After surfacing, the main elements such as Fe, Ni, Cr, Mo, and Nb are distributed regularly in the base metal, heat affected zone, and surfacing layer, and there is segregation of Mo and Nb elements between dendrites. Considering the welding efficiency, dilution rate, and performance of the welding specimen, preheating 200℃ before welding is the best.