The effect of 3d transition metal atom doping on the chloride corrosion resistance of iron-based alloys is different. Under the aqueous solution environment simulated by the VASPsol method, the First-Principles method based on density functional theory was adopted to study the influences of 3d transition metal atoms (Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn) doping on the work function, Cl adsorption energy and electronic structure of the α-Fe(100) surface. The results show that the doping of Sc, Ti, V, Cr, Mn, Co, Ni and Cu atoms can change the work function of the surface to varying degrees, while Zn doping has little effect on it. In the chlorine-containing water environment, the most stable adsorption site of Cl on the α-Fe(100) surface is affected by the atomic number arrangement of the doping atoms. Doping atoms with larger/smaller atomic numbers than Fe atoms reduce/increase the adsorption strength of Cl on the α-Fe(100) surface. The influence of doping atoms on the surface Cl adsorption energy is achieved by changing the bonding strength between Cl and the doped surface.