Mild steel was coated by hot-dipping in a molten aluminum bath. The Fe–Al–Nb alloyed coating was prepared by implanting the Nb atoms into the Fe–Al coating using a double-glow plasma surface metallurgy method. The morphology, element distribution and phase composition of the alloyed layer were characterized by OM, SEM/EDX and XRD. Meanwhile, the basic mechanical properties of these two coatings were measured and compared. The results showed that the Nb element exhibited gradient distribution in the Fe–Al coating. And the alloyed layer consisted of pure Nb, Fe2Al5, Fe3Al, AlNb2 and Fe7Nb6 phases. After Nb addition, the microhardness of the Fe–Al coating was improved for the diffusely distributed carbide phases. And the adhesion was enhanced with better plastic deformation. What's more, the nanoindentation tests indicated that the toughness of the Fe–Al coating was improved with a stronger ability to resist plastic deformation and a greater plastic deformation work.