The invention relates to a preparation method and application of a formation foil, and particularly provides a preparation method of a formation foil. The method comprises the steps that a corrosion foil is subjected to third-stage formation treatment in an ammonium adipate water solution; the corrosion foil after the third-stage formation treatment is subjected to dipping treatment in a phosphoric acid water solution; the corrosion foil after the dipping treatment is subjected to fourth-stage formation treatment in the ammonium adipate water solution; the corrosion foil after the fourth-stageformation treatment is subjected to first heat treatment; and the corrosion foil after the first heat treatment is subjected to fifth-stage formation treatment, so that the formation foil is obtained, and the fifth-stage formation treatment is carried out in an alcohol solution of organic phosphoric acid and ion liquid. Compared with the formation foil in the prior art, the specific volume of theformation foil prepared by the method is not attenuated under the condition that voltage is basically the same, and the water resisting property is enhanced remarkably.