The invention relates to a window film with automatically adjustable light transmittance. The window film is prepared by comprising the steps of adding a photochromic dye, an ultraviolet absorbent agent, a pressure-sensitive adhesive and an organic solvent into a stirrer, unceasingly stirring to raise the temperature to be 50 DEG C, then keeping the temperature, unceasingly stirring for 0.5 hours so as to obtain a photochromic pressure-sensitive adhesive; coating the photochromic pressure-sensitive adhesive on a PET (polyethylene terephthalate) base film, drying the PET base film, and compositing the PET base film coated by the photochromic pressure-sensitive adhesive and the PET base film plated with a thermal-protective layer so as to obtain a composite film; coating an anti-scratch coating on one surface of the composite film, solidifying the anti-scratch coating through a UV-irradiation, coating the pressure-sensitive adhesive one the other surface of the composite film, and compositing the pressure-sensitive adhesive surface and a release film. The window film provided by the invention has the advantages that the regulation range of the visible light transmittance is large, the light transmittance is automatically reduced under the highlight environment and can automatically recover under the low light environment, and the colorless light is changed to be colored under the highlight environment, so that the whole beautiful effect is improved, the color kind and light transmittance increasing and decreasing range are adjusted according to the need, the manufacturing process is simple, and the production efficiency is high.