The present application relates to an electrical engineering mica composite insulation film and a preparation method therefor. The electrical engineering mica composite insulation film comprises a coupling agent-modified lamellar electrical engineering mica powder and a chitosan salt formed by the reaction of an acid and chitosan, wherein the chitosan salt is filled between the oriented lamellar mica powder, in order to form a bionic nacre structure with the chitosan salt as ash and the electrical engineering mica powder as bricks. The preparation method of the electrical engineering mica composite insulation film comprises the following steps: adding an electrical engineering mica powder into an acidic chitosan aqueous solution and mixing same until uniform to prepare an electrical engineering mica powder-chitosan composite solution; removing air bubbles from the electrical engineering mica powder-chitosan composite solution, and drying same to form a film, so as to obtain the electrical engineering mica composite insulation film having a bionic nacre structure with the chitosan salt as ash and the lamellar electrical engineering mica powder as bricks. The electrical engineering mica composite film of the present application has a high strength and toughness, the thickness of an electrical engineering mica tape is reduced and the pressure resistance grade is improved.