PURPOSE: To form a surface structure excellent in external appearance, by forming an Ni or Co layer on the surface of a steel material and then forming a Zn layer on the above so as to improve the adhesive strength between the plating film and the steel material and prevent the occurrence of burning.

CONSTITUTION: As pretreatment, an Ni or Co layer is formed to about 1W10μm film thickness on the surface of a steel material by means of electroless plating or electroplating. Subsequently, hot dip galvanizing, electrogalvanizing, or thermal spraying of metallic Zn is applied so as to form a Zn layer of ≤about 150μm film thickness. This method is applicable to high-tensile steel, silicon- killed steel, etc., and by using this method, physical properties at the surface of a steel material to be used for a building structure, etc., can be strengthened.