The invention discloses an inorganic optical variable ink comprising a pigment, a binder and an assistant, wherein the pigment is a silver-doped lanthanum titanate compound, and can become into brick-red from white under ultraviolet light irradiation. The preparation method comprises the following steps: 1, mixing TiO2, La2O3 and AgNO3 powder/crystal, adding absolute ethyl alcohol to, grinding into a paste, heating and taking out, cooling, grinding into even and fine particles, naturally cooling to room temperature after roasting, carrying out ball-milling, and sieving after baking, so as to obtain La0.9Ag0.1TiO3 particles; 2, preparing a mixed solution from ethyl acetate, ethyecellulose and epoxy resin; 3, adding colloidal calcium, polyethylene glycol, an antidesiccant and a dispersing agent to the mixed solution prepared in the step 2, and evenly mixing; 4, putting the mixed solution evenly mixed in the step 3 into a light-tight ball-milling tank, putting the La0.9Ag0.1TiO3 particles into the ball-milling tank, and taking out after ball-milling.