The invention discloses a preparation method of an anisotropy alginate thin film. The preparation method includes the following steps that sodium alginate is added into deionized water, and a sodium alginate solution is obtained through stirring dissolution and swelling; the surface of a medium is coated with the sodium alginate solution, then another medium covers the upper surface of the sodium alginate solution to be placed in a vacuum oven for standing, and bubbles are removed; then the mixture is placed in a coagulating bath solution to be dispersed; afterwards, the mixture is taken out and dried at an indoor temperature so that the anisotropy alginate thin film can be obtained. The method has the advantages that the technology is simple, large-area production can be achieved, and cost is low; the size and thickness of the thin film can be controlled, the anisotropy of the obtained anisotropy alginate thin film is obvious, the thin film has color stripes when being observed under an orthogonal polarization microscope and has obvious threads when being macroscopically observed, and the thin film can be used on the aspects of decoration, false-proof marks, color coatings, thermosensitive sensors and the like.