Nickel base alloy has good high temperature resistance and corrosion resistance, adopting 625 nickel-based alloy for the overlaying on the surface of carbon steel or alloy steel can guarantees the strength of the base material,ensures the corrosion resistance of material,and saves the material procurement cost. The dilution rate affects the microstructure and mechanical properties of nickel base alloy,also affects the corrosion resistance of the overlaying layer. The effect of postweld heat treatment on the dilution rate of Fe content in overlaying layer is investigated,which supply feasibility solution for production. The Inconel 625 is used for overlaying of different base materials respectively, the thickness of overlaying layer is not less than 3 mm,and it should be at least two layers. And then the postweld heat treatment with or without contrast test is carried out. By comparing and analyzing the Fe element contents in different areas,the results show that postweld heat treatment has no significant effect on the dilution rate of Fe content in overlaying layer. The closer the distance from weld fusion line,the higher the dilution rate of Fe content.