Disclosed is a method of preparing a copper electroplating layer having high adhesion to a magnesium alloy, which is advantageous because the usability of the magnesium alloy, having the highest specific strength among actually usable metals, can be increased through the development of a process of forming a uniform copper plating layer upon electroplating of the magnesium alloy. The method of preparing a copper electroplating layer having high adhesion to a magnesium alloy of this invention is characterized in that the magnesium alloy is pretreated with a plating pretreatment solution to form a film for electroplating, serving as a magnesium alloy pretreatment layer, exhibiting a uniform current distribution, which is then electroplated with copper to form the copper plating layer. According to this invention, through the pretreatment of the magnesium alloy, the adhesion of the copper plating layer to the film for electroplating formed on the magnesium alloy can be increased.